In this chapter, a brief overview of systemic theory is offered within a historical perspective which describes how it has progressed through a number of phases from a relatively modernist and behavioural framework, emphasising patterns and sequences in family interactions, to frameworks which came to foreground shared meaning. The most recent developments focus on the centrality of language and the joint construction of understanding between family members. This has much in common with social constructionist approaches to therapy as described in chapter 5. A systemic approach to formulation is then illustrated through the two case studies of Jack and Janet.