Although the concept of reservation appears in a variety of legal disciplines, we have attempted to reveal in our research how reservation has obtained a distinct meaning in tax law. As is known in Turkish tax law, the tax receivable accrues directly upon the taxpayer’s declaration, with no additional examination being performed by the administration in principle. This principle is also known as the principle of trust regarding taxpayers’ declarations. As a result of this principle of trust, taxpayers are also not permitted to file a lawsuit against their declaration, as specified in Paragraph 2 of Article 378 of the Tax Procedure Law No. 2131 . Reservation has emerged as an exception to the rule and is applied particularly to transactions in which taxpayers are unsure about the taxation process, where contradictory judicial decisions have occurred regarding the basic elements of tax, and where the legal regulations are unclear. Taxpayers make a reservation regarding their tax declaration in order to alleviate the uncertainty in their situation and avoid losing their right to object and right to act. However, the reservation right has a broad scope of practice and has been unable to find any estimated basis in legal regulations, with existing rules being inadequate for addressing the issue. In addition to contradictory judicial decisions regarding the right to make a reservation regarding a tax declaration, numerous conflicts are found to have been brought before the Constitutional Court of the Republic of Turkey through individual applications regarding taxpayer rights. During our research regarding the legal basis of reservation in tax law, we determined some limited regulations in the Tax Procedure Law No. 213 and Administrative Judicial Procedure Law No. 2577. The directive on tax administration is a document that explains how the administration shall implement tax laws and contains the most comprehensive definition of the concept of reservation, referring to an administrative unit expressed as an evaluation desk. As a result of our research, we understand the evaluation desk to have the authority and responsibility for evaluating declarations with a reservation. However, the issues to be evaluated and the period of the evaluation are not specified in the directive. By determining these issues in detail and including them in a tax act rather than a directive, we believe a new dimension can be added to the reservation process. However, the more serious issue currently stand is that these rules are contained in a directive, which cannot be specified as a binding source of tax law. Some of the issues this study examines include the legal nature, scope, and conditions of reservation of the taxpayer. Moreover, the study analyses the relationship between the right to declare a tax reservation and certain fundamental taxpayer rights. As mentioned above, the concept of reservation has obtained a sui generis meaning in tax law. This right can only be exercised in the context of declared taxes. Applying reservation to undeclared taxes results in no consequences similar to declared taxes, of which this study provides the details. In fact, despite the fact that this method is also used to refund a paid amount in undeclared taxes, the reservation would not have an authentic impact because the refund will already be made in line with the provision established in favour of the taxpayer. The most contradictory area regarding reservations has emerged for the question of whether declared reservations submitted after the legal period of declaration grant the right to file a lawsuit. The problem has been partially resolved through the decisions the Turkish Constitutional Court has made on individual applications regarding declared tax reservations submitted after the legal deadline. We are of the opinion that declared reservations submitted after the legal period should also provide the taxpayer with the right to act due to the right to access the court, especially in the presence of reasons that lead the taxpayer to file a lawsuit against the administration. Considering that no legal prohibition is found regarding suing for a declaration adjustment provided after the legal period, we believe legal remedies must be made accessible to taxpayers. Different interpretations are observed to be present in both judicial decisions and the literature regarding whether the taxpayers can declare reservations in the repentance process, which is regulated in Article 371 of Tax Procedure Law. Given the nature and purpose of the institution, we are of the opinion that taxpayers are aware of and regret the consequences of their acts and wish to benefit from the repentance institution in order to avoid further penalties by reporting their acts on their own. In this context, the study concludes the principle of non-self-contradiction, which prohibits taxpayers from filing a lawsuit against their own declarations, also applies to the declarations made within the scope of repentance. Thus, submitting these declarations with reservations that reserve the right to file a lawsuit would be inappropriate. A precedent dispute was brought to the Turkish Constitutional Court through an individual application (Milli Reasürans, Application no: 2016/70, 01.07.2020), and the court made its interpretation in this direction, concluding that no violation of property rights had occurred. Our study aims to look into solutions to issues related to reservation in tax law. As stated, reservation creates a buffer zone for taxpayers against the powerful tax administration by allowing them to reserve the right to object to their declarations and file a lawsuit if necessary. In this sense, reservation is an institution that upholds the principles of the rights to legal remedies and to a judicial review of administrative acts. The current regulations governing the right to make a reservation do not provide adequate assurances in terms of either tax compliance or the basic elements of tax-related transactions within the principle of legality. Although the existence of the reservation institution has been acknowledged by the courts and the administration, this institution requires a detailed regulation, even if taxpayers are assumed to have sufficient information about the reservation’s application. To ensure adequate predictability and to avoid infringing on taxpayers’ rights, how and when a reservation can be brought forward should be clarified. The principles of administrative legality and the of tax legality require a legal basis in this regard. Judicial decisions that dismiss an action regarding tax assessments based on declared adjustments, including reservations submitted after the deadline, violate taxpayers’ rights to property and to a fair trial. The Turkish Constitutional Court’s individual application decisions (i.e., Arbay Petrol decision [Application no: 2015/15104, 04.07.2019], Onur Oral decision [Application no: 2019/15602, 22.02.2022] and Emin Akyol decision [Application no: 2019/4696, 18.01.2023]) ruled that preventing taxpayers from effectively raising an objection regarding tax assessments based on their adjusted declarations imposes an excessive burden on the taxpayers. Even if these decisions are significant in some ways in terms of resolving the problem, tax courts still remain to make rulings that are contrary to the principles of taxation and taxpayer rights. Moreover, as stated by the Turkish Constitutional Court in its decision with regards to the individual application of Teslime Aydoğan (Application no: 2015/4255, 09.06.2020, §§.53-54), failure to resolve a contradiction regarding judicial decisions on a particular issue after a reasonable period of time violates taxpayers’ right to a fair trial. As demonstrated in our study, the right to make a reservation regarding tax declaration is directly related to the fundamental rights of the rule of law, such as the rights to access the court and to property. Hence, clarifying the process of the reservation in clear predictable legal provisions is crucial for preventing contradictory and illegal practices.