Adult educational system is an integral part of lifelong learning. It can be defined as a concept that includes participation in the educational process regardless of whether a person continues a previously started schooling or changes the initial education in order to acquire new abilities, knowledge and skills. Ultimately, the person acquires necessary professional qualifications to enter the labour market. The final goal of this thesis is to compare adult educational systems in Croatia and the United States of America in order to see similarities and differences between them. The method used in the comparison is the work on documentation and comparative analysis method. The criteria for comparing the education system are: legislative frameworks for adult education, main goals of adult education, adult education programs, number of participants, layout of curricula and strategies for adult education, and non-formal and informal adult learning. In addition, international research in the field of adult education conducted in these two countries is listed. Based on a detailed comparison, it is evident that there are similarities and differences between adult educational systems of these two countries, and that those similarities are predominant, especially when it comes to general educational goals of the countries themselves. The similarities in the education systems in these two countries are: sources of funding for adult education institutions, legal frameworks governing the adult education system, general goals that people in the education system want to achieve and active involvement of both countries in international research on adult education. The reasons why people choose to join the adult education system are similar. Differences between the education system in Croatia and the United States are visible in the number of years of students, the method of development and the number of curricula that regulate the curriculum, but also the offer of the adult education programs themselves.