Adults learn in a variety of forms and contexts. Instead of uniform concepts that were previously associated with terms like popular education, adult education, or further education, the idea of "lifelong learning" now emphasizes the diversity of learning locations, learning forms, and learning contexts. This shift also brings traditional notions of adulthood and learning into question. The volume provides an overview of the current state of knowledge in the broad field of adult learning and discusses the questions that arise in educational science discourse. The scattered knowledge about phenomena of adult learning is compiled without making specific formats, such as organized learning in educational events, the default focal point, as has been customary until now.