This chapter will examine a brief overview of obsessive compulsive disorder (OCD) and its defining features. Public perception of OCD over time will then be appraised, from the low awareness that existed throughout much of the early twentieth century to the present, when it is almost fashionable to claim that an individual is ‘a little bit OCD’.

The chapter will then examine what distinguishes ‘normal’ obsessions and compulsions from those that are detrimental to the individual and their functioning. Finally, the chapter explores how obsessions and compulsions may have evolved and how they may give the individual a biological advantage.