The intention of this paper is to explore and develop Wilfred Bion"s theory of groups, and to contribute to its wider application across the social sciences. Bion suggested that groups operate simultaneously in two strictly contrasting ways, based on distinctive mental states, which he called "basic-assumption mentality" and "workgroup mentality". He believed that these mentalities determine a group"s capacity to achieve its purposes. However, the development of these ideas has tended to focus on the regressive tendency in group functioning -on basic-assumption mentality. This paper attempts to redress the balance by ascribing equal importance to the notion of work-group mentality. Firstly, it extends Bion"s framework, developing the concept of the "work group" in parallel with the "basic assumptions"; secondly, it considers the dynamic relationship between these two mentalities, in order, finally, to explore the application of Bion"s ideas via a case example.