This chapter begins with a definition of transdisciplinarity. It then identifies three significant responses to the transdisciplinary problem of how to research the interface between the psychological and the sociological: a psychosocial "factors and variables" approach, critical and discursive social psychology, and psychoanalytical psychosocial studies. The second section aims to move the debate forward through the idea of the paradox of the psychosocial. After a discussion of human suggestibility, this paradox is summarized as follows: we both must and cannot separate the psychological from the social. Drawing on the work of Winnicot and Mead, the third section makes the case that we encounter the paradox of the psychosocial during experiences of liminality, and that these experiences are to be understood by means of process thought. The final section introduces the main arguments of the book.