This book comes as one of the outcomes of the COST Action “LUDI – Play for children with disabilities” (2014-2018), a multidisciplinary network including more than 32 countries and 100 researchers and practitioners from the humanistic and technological fields, devoted to study the topic of play for children with disabilities. The primary objective of this book, developed within the scientific activities of the Working Group no. 1, is to review the state of the art of knowledge on play evaluation and to present and discuss existing tools and methodologies for play assessment. Gathering all the existing knowledge in this area of study is urgent; moreover, this knowledge must be harnessed for an innovative goal, potentially disruptive in the overall conception of disability. In fact, it concerns the need to give children with disabilities the opportunity to play as they want, as they wish, in an autonomous way. Establishing the goal of respecting the play for the sake of play of children with disabilities means building an authoritative, appropriate and competent area in favour of these children’s needs.