The behavior of people on the autism spectrum and with other neurodevelopmental disorders often appears incomprehensible, not only to outside observers, but sometimes also to their relatives, therapists or researchers. In order to be able to better understand the meaning, purpose and cause of these people's behavior, it is necessary to know what and how to observe and what meaning to give to what is observed. Therefore, it is necessary to prepare precise, sensitive and reliable diagnostic tools. At the same time, the more precisely we, as researchers and practitioners, are able to describe the functioning of people with neurodevelopmental conditions, the more appropriate therapeutic methods and tools we can design for these people. The aim of this Method Collection is to collect current research reports in the field of diagnostic and therapeutic methods dedicated to people on the autism spectrum and with other neurodevelopmental conditions.