This monograph offers the first comprehensive English-language analysis of the foundational role of the concept of free will across the entire spectrum of Ukrainian civil law. Moving beyond traditional philosophical debates, it examines free will as a core legal idea underpinning key principles and institutions, including personal non-property rights, property law, contractual and non-contractual obligations, intellectual property, and inheritance law. Viktor Savchenko argues that understanding the legal nature and manifestation of free will is crucial for resolving contemporary challenges in civil law, particularly concerning personal autonomy, consent, liability, and the balance between individual choice and legal regulation. Drawing on historical-philosophical analysis and a detailed examination of Ukrainian legislation and doctrine within the broader European continental tradition, the work demonstrates how the concept of free will shapes legal relationships. It provides a unique perspective on a universal legal concept, offering valuable insights for scholars of civil law, comparative law, legal theory, and East European legal systems.