This paper draws together cognitive and socio-cultural constructivist theories to propose a view of adult development as a product of participation in different and overlapping social practice during individuals' life histories. Together, these theories offer a view which emphasises mutuality between social and cultural sources of knowledge and individuals' representations of knowledge. This view sees individuals as constructors of knowledge, but how and what they construct is socially-determined. Ongoing problem-solving in different social practice is the process of knowledge construction and cognitive development underpinning this view. That is, developmental consequences arise from engaging in social practice and in different ways, during individuals' ontogenies (personal histories). Central to the construction of knowledge and cognitive development (with its conceptual, procedural and dispositional components) is individuals' participation in communities of practice (eg. workplaces, home, recreational clubs). In these communities, the qualities of participation and guidance determine how and what knowledge individuals construct. These qualities comprise: (i) the type of activities (routine - non-routine); (ii) existing knowledge base associated with activities (includes interest); (iii) direct and indirect guidance (proximal-distal); (iv) access to and standing in the community (peripheral to fuller participation); and (v) duration of participation. The view of adult development proposed here includes dispositional attributes of values and beliefs held to be inherent within cognitive structures. Hence, aspects of moral and personality development are incorporated in this view of development, thereby reconciling views of development which are sometimes treated separately.