The path to full membership of Republic of Croatia in European Union was not at all easy and prompt. Croatia had to fulfill all prerequisites and satisfy all political, economic, legal and administrative criteria for admission to membership of European Union established in Copenhagen in 1993. In addition to having to convince the members of the European Union at the time that it has a stable democracy and the rule of law along with functional economy accepting the legal acquis of European Union, Croatia had to diplomatically overcome all other challenges and obstacles imposed by the environment. This thesis analyzes the process of admission of Republic of Croatia to European Union from the perspective of meeting the conditions for admission and the challenges that are set in front of Croatia in order to become a member of European Union. The paper apostrophizes the resolution of the chapters whose closures were a condition for Republic of Croatia's entry into European Union, especially chapters 11, 12 and 13, which related to agriculture and fisheries, in which the responsible line ministry made the biggest contribution. It also describes the situations and obstacles faced by Croatian Government and its diplomacy during the complex work of closing certain chapters and adapting national legislation, especially in the field of agriculture and fisheries. The aim of this thesis is not to show only how Republic of Croatia met all the criteria in joining European Union and resolved obstacles confronted along the way through diplomatic means, but also how Croatia in today's circumstances of rapid sociological and political changes in Europe and the world follows the guidelines of European Union legislation and implements its goals and core values.