This chapter focuses on understanding health psychology in the wider system. The main aim is to show the interdisciplinary reach of health psychology and to highlight the importance of inter-connectivity and collaborative working. Initially, synergies and differences between health psychology and other practitioner psychology branches will be discussed. The chapter will then focus outwards on the connection of health psychology with the biopsychosocial sciences. We focus in particular on behavioural, social, and medical sciences. The chapter will conclude with a discussion on the role health psychology plays and could play in multi-, inter-, and trans-disciplinary teams.