Schema therapy could have very easily been named as ‘needs therapy’, so central is the concept of core emotional needs to the practice of modern schema therapy. Borrowing from the basic needs concept and theories of attachment that had been well developed in the developmental psychology literature, Young described the following core domains as pivotal to understanding problems that emerge in the developmental period: (1) Secure attachments to others (includes safety, stability, nurturance, and acceptance); (2) Autonomy, competence, and sense of identity; (3) Freedom to express valid needs and emotions; (4) Spontaneity and play; (5) Realistic limits and self-control. Need satisfaction during childhood leads to the development of healthy schemas and related functional affective and behavioural patterns, while early need frustration leads directly to the development of early maladaptive schemas (EMS) and related negative patterns of behaviour and maladaptive coping styles. This chapter describes the central theories and concepts which underpin schema therapy practice including the original set of eighteen schemas, as well as schema modes and the schema mode model.