Most theoretical approaches to explain human behaviour tend to follow one of two implicit reductionist models: either the causes of behaviour are reduced to inborn and acquired individual traits or reduced to permanent or momentary social influences and categories (Lewis, 2000). Occasionally some minds are able to challenge the reductionist paradigms and achieve “binocular visions”, developing models embracing both the individual and their social environment, as well as their complex interactional dynamics.2 Among these are pioneers such as Sigmund Freud and Adolf Meyer (see Bowlby, 1988), and undoubtedly also Wilfred Bion and Kurt Lewin. The most distinctive assumption shared by Lewin and Bion is that individual and group behaviour are truly indissociable, and should be understood as a dynamic whole in a way similar to the figure/ground reversal phenomenon of optical perception (Bion, 1949b [1961], pp. 86-87; 1951 [1961], p. 134; 1970, p. 66; Lewin, 1935a, p. 3). Based on this assumption, they achieved and inspired groundbreaking integration of the psyche and the social to improve human relations and development in a broad range of social units and institutions (Allport, 1948 [1951]; de Board, 1978; Trist, 1985; Trist and Murray, 1990a, 1993, 1997; Thelen, 1985; Schermer, 1985; Khaleelee and Miller, 1985; Hinshelwood, 1999). The aim of this chapter is to illustrate that Kurt Lewin’s pioneering work on group dynamics influenced some of Bion’s psycho-social concepts and was a solid bridge which assisted Bion in combining his innovative ideas on psychiatry and psychoanalysis with group phenomena and social science. Hence, some of Bion’s concepts on the psycho-social can be seen in the light of Lewin’s models, enriching the contributions of both authors to the comprehension of the complexity of human psycho-social dynamic systems.3