Professionals in the social and health sectors are always striving to establish and maintain contact with their clientele due to their professional self-understanding. However, some clients or entire client groups prove to be resistant; they are difficult to reach. The authors of this book explore the various reasons for the issues of inaccessibility, which can arise in both institutional and personal contexts. At the same time, they outline approaches for engagement and define previously overlooked target groups from the perspectives of different disciplines and practice fields. Lastly, the book questions how well the professional services meet the actual needs of the respective clientele and how to achieve a better participatory practice. The book is dedicated to the social medicine expert Prof. Dr. Brigitte Geiss.