This thesis is devoted to the organizational and pedagogical foundations of the European Students' Union (ESU) activity as a subject of the Bologna process (BP) and outlining opportunities for the creative use of elements of the progressive European experience in terms of the higher education modernization in Ukraine. The research provides, firstly, a thorough analysis of the concepts and terminology, identifies the major determinants of the European higher education integration. Modernization is proved to be the concept which reflects the whole range of quality changes in the European higher education and presupposes the engagement of different subjects (society, Ministers responsible for higher education, universities, the business community and students) into the process of decision-making. Secondly, the thesis clarifies theoretical foundations of student engagement into the process of higher education modernization, identifying three major aspects of studying this notion: socio-political, academic and administrative. Thirdly, it defines four stages of the development of the ESU as a subject of the BP and highlights the structural, procedural and content foundations of the organization's activity. Besides, it characterizes the peculiarities of the biggest and most influential National students' unions (NUSes), members of the ESU. Finally, it summarizes productive experience of student engagement on the European and national levels, outlining the opportunities to be used in the aspect of the studied problem in Ukraine. The scientific novelty and theoretical significance of the obtained results of the research are the following: for the first time in Ukrainian Pedagogy a comprehensive study of the European Students' Union as a subject of the Bologna process was held; the conceptual foundations of student engagement into higher education governance were characterized. The stages of the ESU's development as a supranational subject of the Bologna process were defined. The organizational foundations of the ESU's activities in the context of the Bologna Process were outlined (objectives, priorities, the organizational structure, policy, basic principles, mechanisms of cooperation with other supranational organizations). The main areas of the ESU's engagement were analyzed (quality assurance, financing of higher education, student-centered paradigm, students' unions development and engagement into the higher education modernization process, graduates' employability). Forms and means of the ESU's influence on the decision-making process in higher education were highlighted. The case study of the largest NUSes helped analyze the progressive aspects of student engagement, which can be used in the context of higher education modernization in Ukraine. On the basis of the ESU's achievements the model of student engagement into the higher education modernization in Ukraine was developed. The practical significance of the results of the research lies in the fact that main findings and conclusions can be used by politicians, university administrative staff and student leaders in the course of student engagement system development in Ukraine. The prognostic potential of the researches increases the possibility of using the results for further studies on higher education governance and improving the mechanisms of engaging all actors into this process.