Psychological development is a dynamic process, which begins at birth and proceeds in an ascending order through a series of sequential stages manifesting into various characteristic behavior. These stages are governed by genetic, familial, cultural, interpersonal and inter-psychic factors. Child psychology deals with the mental power or an interaction between the conscious and subconscious element in a child. Theories of child psychology are broadly classified into two groups—psychodynamic theories and behavioural theories. The stages of child development and basis of various behaviour patterns are explained in this chapter through a description of the various theories of child psychology.