Abstract
<jats:p>This article examines the principle of party autonomy as one of the key institutions of private international law and international commercial transactions. It explores the historical stages of the formation of this principle, its legal nature, and the relationship between its substantive-law and conflict-of-laws elements. Particular attention is paid to the implementation of party autonomy under the legislation of the Republic of Kazakhstan, especially Article 1091 of the Civil Code of the Republic of Kazakhstan. The paper substantiates the mixed legal nature of party autonomy, combining freedom of contract with the conflict-of laws function of choosing the applicable law. It identifies the main law-enforcement issues related to determining the true intention of the parties, the limits of permissible choice of law, the operation of mandatory rules and public policy, as well as the development of digital and cross-border contractual relations. The study concludes that there is a need for further improvement of national legislation and for the development of uniform criteria for assessing the admissibility of the choice of applicable law in international commercial relations. </jats:p>