This paper outlines some of the basic issues in evolutionary thinking when applied to psychopathology. It aims to give some background and context to the papers that follow. Particular attention is given to the way evolution is constrained by previous design features, the importance of trade offs between advantages and disadvantages of different traits, the way social dilemmas and conflicts have shaped the evolution of human motivational systems, and the psychology that supports them. The paper concludes with a plea to avoid thinking of evolutionary approaches as a reductionist science, when the focus needs to be on the way evolution theory informs the study of the social-biological interface.