Cognitive behaviour therapy (CBT) is derived from both behavioural and cognitive theories. Using concepts such as operant conditioning and reinforcement, behavioural theories treat behaviour as explicable without recourse to description of mental activity. In contrast, mental activity is central to all concepts derived from cognitive psychology. Both sets of theories have been of value in explaining psychological disorders and, in the design of interventions they have proved an effective combination. Central to that part of cognitive theory that is relevant to CBT is the concept of ‘schemas’, first described in detail by Jean Piaget. A schema is a mental ‘structure for screening, coding, and evaluating impinging stimuli’. The origin of mental schemas lies in the pre-verbal phase when material is encoded in non-verbal images that, as the child's language develops, gradually become verbally labelled. They form part of a dynamic system interacting with an individual child's physiology, emotional functioning, and behaviour with their operation depending on the social context in which the child is living. There are similarities but also differences between schemas and related concepts in psychoanalysis, such as Freudian ‘complexes’ and Kleinian ‘positions’. Schemas can be seen as organized around anything in the child's world, especially objects, beliefs, or emotions. They develop from past experience. The processing of new information in relation to such schemas can usefully be seen as involving the evaluation of discrepancies between information that is received and information that is expected. If there is a discrepancy, (the information not corresponding with that expected), then during the coding process information may be distorted so that it no longer creates discomfort, or, more adaptively, it may be incorporated into a modified schema.