The present review aimed to analyze the scientific literature untill 2010 about the theories of Obsessive Compulsive Disorder in order to make clear how a biological and cognitive hypotheses might be integrated in a comprehensive point of view. In the analysis, at biological level were included neuroanatomic and neurophysiologic models and animal models; instead at cognitive level were included different theories of Salwoskies, Van den Hout, Mancini e Rachman. Biological, cognitive, and behavioral elements of the theories have to be clearly distinguished between specific and general conditions, as do critical past events and current trigger conditions. The theories compared were drawn from the neurobiological, cognitive, and behavioral literature that proposed empirical supported models. We conclude that there are substantive differences among the cognitive theories and between the biological theories reviewed. However, cognitive and biological theories appear to be compatible in principle. It is not clear whether substantive differences among theories are due to the existence of subtypes of OCD or due to the predominance of multifactorial cause. It is argued that current treatment methods imply particular theories, and that particular patterns of success and failure can be understood in relation to theory through the methods we have employed.