The monograph presents the results of the research on development of key competences of adults executed in implementation of the research project funded by the Research Council of Lithuania „Platform of adult key competence development“. The goal of research is to provide holistic evaluation of the key competence development of adults in Lithuania. There were analysed the following core key competences: communication in the native and foreign languages, development of cultural awareness, entrepreneurship, application of information society technologies, learning to learn. Research disclosed increasing impact of key competences for the employment, sustaining of workplaces, career, civic life and personal development of adults in Lithuania, as well as increasing awareness of the importance of development of these competences.