The inheritance agreement, as explicitly stated in the Turkish Civil Code, is a special type of legal transaction characterized as a "disposition upon death". These agreements aim to ensure that all the material and moral assets owned by an individual during their lifetime are transferred to their desired person or persons, in the determined proportions or under specified conditions, upon their demise. Although an inheritance agreement is a legal transaction carried out by the testator while alive, its provisions and consequences arise only upon the testator's death.

The primary purposes for entering into inheritance agreements can vary. These include preemptively averting potential future disputes among prospective heirs, ensuring the fair distribution of assets in accordance with the testator's wishes, securing the transfer of family businesses or specific significant assets to particular individuals, regulating rights arising from inheritance law in special circumstances such as adoption, or reinforcing special legal relationships between spouses through inheritance provisions. Ultimately, inheritance agreements provide a legal framework for the testator's will, allowing them to determine the future fate of their assets in advance.

1. Types of Inheritance Agreements

Inheritance agreements can manifest in different forms depending on the testator's desires and objectives. The Turkish Civil Code primarily divides inheritance agreements into two main categories: positive inheritance agreement and agreement of renunciation of inheritance.

In a positive inheritance agreement, the testator can directly appoint the other party to the agreement as an heir or bequeath a specific asset to them. Similarly, the testator can, through an agreement with the other party, appoint a third person as an heir or leave a specific asset to a third person. These types of agreements actively regulate the transfer of the testator's assets to specific individuals.

The agreement of renunciation of inheritance, also known as a negative inheritance agreement, involves a person who could potentially be an heir renouncing their right to inheritance, either for a consideration or without consideration, while the testator is still alive. This agreement may aim to ensure that the testator's assets remain with specific individuals in a greater proportion or to reduce the number of heirs.

Inheritance agreements are also subject to a distinction between unilateral inheritance agreements and bilateral inheritance agreements. This distinction is based on whether only one party or both parties make a disposition upon death in the agreement. Another important distinction is between onerous inheritance agreements and gratuitous inheritance agreements, depending on whether one of the parties to the agreement undertakes an inter vivos obligation.

• 1.1. Unilateral and Bilateral Inheritance Agreement

A unilateral inheritance agreement legally refers to an agreement where only one party makes a disposition upon death. In this type of agreement, only the testator performs a disposition. This disposition can be in the form of appointing the other party to the agreement or a third party not involved in the agreement as an heir, or bequeathing specific assets. The other party to the agreement may be obliged to accept this unilateral declaration of intent by the testator. However, in some cases, this acceptance may involve an undertaking to pay a fee, thereby creating an obligation. At this point, the existence of a payment undertaking can transform the initially unilateral inheritance agreement into an onerous structure. Therefore, a unilateral inheritance agreement essentially represents a legal relationship based on the testator's active disposition and the other party's passive acceptance.

A bilateral inheritance agreement occurs when both parties mutually make dispositions upon death. Essentially, in this type of agreement, there are legally two separate inheritance agreements. However, these two separate declarations of intent are combined under a single agreement text, allowing the parties to make dispositions upon death in favor of each other. The most typical example of this situation is when spouses appoint each other as heirs. In this case, each spouse makes a separate disposition upon death appointing the other as their heir. However, these two dispositions are usually expressed in the same agreement text and give rise to interconnected legal consequences. The requirement that both parties have full legal capacity at the time of the agreement is of critical importance for the validity of bilateral inheritance agreements.

• 1.2. Onerous and Gratuitous Inheritance Agreement

An onerous inheritance agreement refers to the type of agreement where one party makes a disposition upon death, and in return, the other party agrees to pay a consideration or perform another act. In these types of agreements, there is a direct legal link or causal relationship between the testator's disposition and the obligation undertaken by the other party. For example, the testator appointing a person as an heir and that person undertaking to pay a certain amount of money to the testator constitutes an example of an onerous inheritance agreement. Here, the testator's disposition of appointing an heir and the other party's payment undertaking are interdependent.

An agreement of renunciation of inheritance can also be onerous in certain situations. If the testator agrees to pay a consideration, and in return, the heir renounces their future inheritance right, it is an onerous agreement of renunciation. For instance, if the testator gives an apartment to one of their heirs during their lifetime, and that heir, in return, waives their future inheritance right, this can be an example of such an agreement. Onerous inheritance agreements aim to establish a balance of mutual interests between the parties.

A gratuitous inheritance agreement is a type of agreement where the testator makes a disposition upon death, and the other party only accepts the testator's will without undertaking any debt or obligation. In gratuitous inheritance agreements, the testator's unilateral declaration of intent is fundamental, and it gives rise to legal consequences upon the other party's acceptance of this declaration. These types of agreements may include matters such as the determination of heirs according to the testator's will or the bequest of a specific asset to a person. However, the other party is not required to pay any material or moral consideration to the testator. Gratuitous inheritance agreements generally reflect the testator's desire to transfer their assets gratuitously to their relatives or desired individuals.

2. Parties and Legal Capacity in Inheritance Agreements

An inheritance agreement fundamentally has two parties: the testator who makes the disposition upon death regarding their assets, and the other party to the agreement who is the recipient of this disposition. The other party to the agreement can be one of the heirs or a third person with no kinship ties to the testator. The legal capacity of the parties is of vital importance for the validity of the agreement. Article 503 of the Turkish Civil Code explicitly states the mandatory conditions that a person making an inheritance agreement must meet:

• The person making the inheritance agreement must have discernment, meaning their mental faculties must be sound, and they must be able to understand the legal consequences of their actions..
• The person making the inheritance agreement must be of age, meaning they must have completed eighteen years of age.
• The person making the inheritance agreement must not be under guardianship, meaning their legal capacity must not have been restricted by a court decision.

In this context, having full legal capacity is generally mandatory to enter into an inheritance agreement. However, this applies to the party making the disposition upon death in the inheritance agreement (the testator). If both parties make dispositions upon death in the agreement, i.e., in the case of a bilateral inheritance agreement, both parties must have full legal capacity at the time of the agreement. On the other hand, if the other party to the agreement does not make a disposition upon death but only accepts the testator's will or undertakes to pay a consideration in an onerous inheritance agreement, the legal capacity of the party not making the disposition upon death is subject to the general rules of legal capacity:

• If this party is fully legally incapacitated (e.g., minors permanently lacking discernment or persons under guardianship), the inheritance agreement is made on their behalf by their legal representative (guardian or custodian). However, if the fully legally incapacitated person is under guardianship, the separate consent of both the magistrate's court and the civil court of first instance is mandatory.
• If this party is partially legally incapacitated (e.g., minors over eighteen years of age with discernment), and the inheritance agreement does not impose an inter vivos onerous debt on them (i.e., they only accept the testator's disposition), they can enter into the agreement alone without the involvement of their legal representative (guardian). However, if the partially legally incapacitated person will incur a debt under the inheritance agreement, i.e., if an onerous inheritance agreement is being made, their legal representative must personally participate in the transaction.

3. Formal Requirements for Inheritance Agreements

For inheritance agreements to be valid, the legislator has prescribed special and strict formal requirements. These formal requirements are explicitly regulated in Article 545 of the Turkish Civil Code:

"For an inheritance agreement to be valid, it must be drawn up in the form of an official will. The parties to the agreement simultaneously declare their wishes to the official, and sign the drawn-up agreement in the presence of the official and two witnesses."

The official mentioned in the law is, in practice, accepted as a Notary Public. Therefore, an inheritance agreement can only be made in writing before a Notary Public. Inheritance agreements made in simple written form or orally are absolutely invalid. This formal requirement has been established due to the importance of inheritance agreements, to ensure the healthy determination of the parties' wills and to prevent potential future legal disputes.

On the other hand, the right to enter into an inheritance agreement is a strictly personal right, so it is not possible to carry out this transaction through a representative. That is, the testator must personally appear before the Notary Public to conclude the inheritance agreement. In contrast, the party renouncing inheritance does not make a disposition upon death, so they can carry out this transaction through a representative. Therefore, the personal presence of the person renouncing inheritance before the notary public is not mandatory.

4. Validity of Inheritance Agreements

Although an inheritance agreement exists legally, it generally produces its provisions and consequences only upon the testator's death. The agreement has no application while the testator is alive. Furthermore, since an inheritance agreement is a bilateral legal transaction, it is binding between the parties to the agreement. According to this principle, unilateral withdrawal from an inheritance agreement is generally not possible. However, certain special situations and exceptions by law may exist, and therefore the specific conditions of each individual case must be carefully examined.

5. Dispositions Upon Death That Can Be Made Through an Inheritance Agreement

Through a validly concluded inheritance agreement, the testator can make various dispositions upon death regarding their assets after their demise. The Turkish Civil Code lists the main transactions that can be made through an inheritance agreement as follows:

• Appointment of an heir (TCC Article 516): The testator can appoint one or more persons other than their legal heirs as heirs through an inheritance agreement. These appointed heirs have the same rights and obligations as legal heirs.
• Bequest of a specific asset (TCC Article 517): The testator can bequeath a specific asset from their estate (e.g., real estate, a vehicle, a painting, etc.) to one of their heirs or a third person who is not an heir through an inheritance agreement. In this case, the legatee has the right to demand the delivery of this asset upon the opening of the inheritance.
• • Imposition of conditions and obligations (TCC Article 515): The testator can attach certain conditions to the dispositions upon death they make through an inheritance agreement or impose certain obligations on the heirs/legatees. For example, an heir may be made an heir on the condition of completing a specific education, or a legatee may be obligated to make a donation to a specific charity..
• Appointment of a substitute heir (TCC Article 520): The testator can appoint a substitute heir in an inheritance agreement in case the first appointed heir cannot become an heir for any reason (e.g., predeceases the testator or rejects the inheritance). This prevents the inheritance from remaining uncertain.
• Appointment of a successive heir (TCC Article 521): The testator can appoint a primary heir and a successive heir to whom the inheritance will pass upon the death of the primary heir or the occurrence of a specific event through an inheritance agreement. This arrangement aims for the assets to be used by certain individuals for a specific period and then transferred to others.
• Establishment of a foundation (TCC Article 526): The testator can declare their intention to establish a foundation and specify the foundation's assets and purpose through an inheritance agreement. However, the legislator has introduced a special provision in this regard: even if the establishment of a foundation is done through an inheritance agreement, it is not binding, meaning the testator can unilaterally withdraw from establishing the foundation at any time. This exception aims to allow the free modification of the intention to establish a foundation until the moment of death.
• Disinheritance (TCC Article 510): The testator can disinherit one of their legal heirs if certain justified reasons listed in the law exist. The disinherited person loses their share of the inheritance and the right to file a reduction lawsuit. However, this action is also not binding on the testator; that is, the testator can unilaterally withdraw the disinheritance at any time. This is also related to the principle that the testator's will is valid until the moment of death.

6. Dispositions Upon Death That Cannot Be Made Through an Inheritance Agreement

The testator can appoint anyone they wish as an heir through an inheritance agreement and can also carry out the other dispositions upon death listed above. However, inheritance law includes the concept of reserved share, which is a portion legally reserved for certain legal heirs. If the testator has legal heirs with a reserved share, such as their descendants (children, grandchildren), parents, or spouse, the testator can freely dispose of only the portion remaining after deducting these individuals' reserved shares (the disposable portion).

The disposable portion is the amount obtained by subtracting the total of the reserved shares from the entire estate. The reserved share ratios are determined by law according to the groups of legal heirs. For example, the reserved share of descendants is half of their legal inheritance share, the reserved share of parents is one-quarter of their legal inheritance share, and the reserved share of the spouse varies depending on their relationship with the testator's other heirs.

If the testator has none of the aforementioned legal heirs with a reserved share, they can freely dispose of their entire estate. The institution of reserved share aims to protect the minimum rights of certain close relatives over the inheritance and prevents the testator from making dispositions that completely eliminate these rights. Dispositions made through an inheritance agreement are also subject to the rules of reserved share, and dispositions that violate reserved shares can be limited by a reduction lawsuit filed by the heirs.

7. Termination and Annulment of Inheritance Agreements

The termination or invalidation of an inheritance agreement can occur in various ways. These situations range from the termination by the common will of the parties to the agreement, to special grounds for termination and withdrawal by law, and finally to the annulment due to legal defects.

• 7.1. Termination of the Agreement by Agreement of the Parties

An inheritance agreement can always be terminated by the written agreement of the parties. In this case, the common will of both parties to terminate the agreement is essential. The legislator has not made it mandatory for this written agreement to be made before a Notary Public; it is sufficient for it to be made in simple written form between the parties. This provision allows the parties to terminate the legal relationship they established by their free will with the same free will.

• 7.2. Termination and Withdrawal from the Agreement

Since inheritance agreements are bilateral legal transactions, they generally cannot be unilaterally terminated due to the principle of the binding nature of contracts. One party unilaterally dissolving the agreement is contrary to the principles of legal certainty and trust in contracts. However, the legislator has allowed the testator to unilaterally withdraw from or terminate the agreement in certain limited cases. These exceptional situations are as follows:

• Withdrawal in Case of Grounds for Disinheritance: If the testator has the right to disinherit the other party to the inheritance agreement or a third person appointed as an heir in the agreement based on one of the justified reasons listed in Article 510 of the Turkish Civil Code, the testator can unilaterally withdraw from the previously concluded inheritance agreement. This withdrawal is carried out by a new will drawn up by the testator in official form (before a notary public). In this will, the testator explicitly states that they are withdrawing from the inheritance agreement and justifies the reason for disinheritance. In this case, the testator's subsequent and officially expressed will invalidates the relevant provisions of the previous inheritance agreement. However, whether the reason for disinheritance is legally valid can be challenged by interested parties after the opening of the inheritance.
• Withdrawal in Case of Non-Performance of Counter-Performance in an Onerous Inheritance Agreement: If the inheritance agreement in question is onerous, i.e., if it is stipulated that the other party to the agreement will perform a certain act (payment of a consideration, performance of a service, etc.) in return for the testator's disposition upon death, and this act is not duly performed by the other party, the testator can exercise their right to withdraw from the agreement within the framework of the general provisions of the law of obligations. In this case, a clear and unequivocal declaration of the testator's intention to withdraw must reach the other party to the agreement. Upon the other party's receipt of the declaration of withdrawal, the onerous inheritance agreement terminates with retroactive effect, and the parties are obliged to return what they have mutually received. However, if the obligated party offers to perform their act belatedly, even after the declaration of withdrawal has reached them, and at the same time provides sufficient security to cover the testator's damages, the testator's right to withdraw from the agreement may be prevented. This provision aims to protect the balance of mutual interests between the parties in onerous agreements and the principle of the binding nature of contracts.
• 7.3. Annulment of the Agreement

The annulment of an inheritance agreement means that, although it was validly established, it is retroactively eliminated by a court decision due to the existence of certain legal grounds by law. The main situations that require the annulment of an inheritance agreement are as follows:

• Dispositions upon death and donations contrary to the agreement: If the testator, after concluding a valid inheritance agreement, makes other dispositions upon death (e.g., drawing up a new will) or inter vivos donations that contradict the provisions of this agreement, the annulment of the inheritance agreement can be requested. However, this annulment requires a lawsuit to be filed after the testator's death. The testator's dispositions contrary to the agreement while alive do not in themselves invalidate the inheritance agreement. The right to file an annulment lawsuit belongs to those whose interests are harmed by the inheritance agreement.
• Defect of will: Inheritance agreements must be established with the free and healthy will of the parties. If the testator's or the other party's will was defective at the time the agreement was concluded (e.g., due to reasons such as mistake, fraud, or duress), the inheritance agreement can be annulled.
• Lack of legal capacity: If the testator did not have full legal capacity (lack of discernment, minority, or being under guardianship) at the time the inheritance agreement was concluded, the inheritance agreement can be annulled. Similarly, if a bilateral inheritance agreement is involved and the other party also makes a disposition upon death, both parties must have full legal capacity at the time of making the agreement; otherwise, the agreement can be annulled due to lack of legal capacity.

In the case of lack of legal capacity, the inheritance agreement does not automatically become void; it produces its effects as if it were a valid agreement upon the testator's death. If it is desired that these provisions not be valid, the interested party (e.g., legal heirs) must file an annulment lawsuit. Certain periods of limitation are by law for this annulment lawsuit:

• A one-year period of limitation begins from the date the plaintiff learns both that they are entitled to the inheritance, and of the disposition upon death and the grounds for annulment. However, if all these facts were learned during the testator's lifetime, the period begins to run from the testator's death.
• If these circumstances cannot be learned within ten years, the right to file a lawsuit is forfeited; however, this applies if the defendant is in good faith.
• If the defendant is in bad faith (e.g., obtained the inheritance knowing about the lack of capacity or by causing a defect of will), the period for learning about these circumstances and filing a lawsuit is twenty years. These periods aim to ensure legal certainty and the conclusion of lawsuits within a reasonable time.

8. Fundamental Differences Between Inheritance Agreements and Wills

Although both wills and inheritance agreements are dispositions upon death made by the testator regarding the distribution of their assets after their death, they differ significantly in terms of their legal nature, form of execution, and consequences. The fundamental differences between these two legal institutions can be summarized as follows:

• Requirements for Legal Capacity: To make a will, according to the Turkish Civil Code, it is sufficient to have completed fifteen years of age and have discernment. That is, it is not mandatory for the person making the will to have full legal capacity. However, full legal capacity is required for an inheritance agreement. This means that the person making an inheritance agreement must have discernment, be of age, and not be under guardianship. The stricter requirements for legal capacity for inheritance agreements arise from the fact that these agreements establish a binding legal relationship between the parties.
• Form of Execution: A will can be made in three different forms by the Turkish Civil Code: oral will, official will and holographic will. This variety allows the testator to make dispositions according to different situations and preferences. In contrast, an inheritance agreement can only be made in official form. This means that for the validity of an inheritance agreement, it must necessarily be drawn up before a notary public. The stricter formal requirement for inheritance agreements compared to wills aims to ensure that this agreement, which is binding on the parties and definitively regulates the future fate of the assets, is executed with due formality and certainty.
• Modification and Revocation: In a will, the testator has the freedom to modify or revoke their will at any time and unilaterally while alive. The will reflects the testator's last wishes and can therefore always be changed or withdrawn. However, an inheritance agreement is based on an agreement between the parties. Therefore, the modification or revocation of an inheritance agreement is only possible with the mutual consent of the parties. Unilateral withdrawal from or modification of an inheritance agreement is generally not possible (except for the special cases mentioned above). This fundamental difference shows that an inheritance agreement has a stronger binding effect than a will. The legal relationship established by an inheritance agreement is protected by the common will of the parties and is more resistant to unilateral interventions.

In conclusion, inheritance agreements and wills are two important instruments of disposition upon death in inheritance law, but they show significant differences in terms of requirements for legal capacity, form of execution, and especially the possibility of modification/revocation. It is of great importance for testators to carefully evaluate the differences between these two instruments and choose the one that best suits their specific circumstances when regulating the fate of their assets after death. Obtaining legal advice is a critical step in making a correct and valid disposition upon death.