Convention on the Rights of Persons with Disabilities (CRPD) Article 12’s knock-on effects are analysed primarily from the legal point of view, but with all due regard for its psychological, psychiatric and diagnostic ramifications. The CRPD affects traditional paradigms of legislations concerning the capacity of persons with disabilities to perform legal acts. When the CRPD was adopted, the protection of persons with disabilities in the field of capacity to perform legal acts was mainly based in many countries on a substitute decision-making model. The importance and scope of application of the assisted (supported) decision-making model applied was limited and narrow. The CRPD, in particular its Article 12, requires that this state of things should be changed and improved in order to reduce the scope of application of the substitute decision-making model to the maximum possible extent. The chapter also presents an overview on the key concepts discussed in this book.