This document discusses the etiology and pathogenesis of obsessive compulsive disorder (OCD). It covers biological, psychological, and social causal factors. Key points include: OCD is associated with abnormalities in brain circuits involving serotonin, dopamine, and glutamate; it has a significant genetic component with heritability estimates around 45-65%; brain imaging studies have found structural and functional differences in brain regions involved in these circuits in individuals with OCD compared to controls. The document provides a detailed overview of the understanding of OCD pathogenesis.