A summary of the Third International Obsessive-Compulsive Disorder Conference proceedings on neuroimaging research and neurocircuitry models of obsessive-compulsive disorder (OCD) is presented. This survey of recent and ongoing research indicates that a wide range of modern techniques and experimental strategies are being employed in a complementary fashion to enhance our understanding of OCD. Imaging studies in animal models of OCD are helping to elaborate relevant normal anatomy and neurochemistry. Functional imaging methods are being employed in conjunction with behavioral, pharmacologic, and cognitive challenge paradigms. Magnetic resonance spectroscopy as well as radiotracer methods are being utilized to measure neurochemical and neuropharmacologic indices in OCD. Transcranial magnetic stimulation has emerged as a tool for probing neurocircuitry that may also have therapeutic potential. Experimental designs and data-analytic methods are evolving to help elucidate the pathophysiology of OCD and related disorders, delineate neurobiologically meaningful subtypes of OCD, and identify potential predictors of treatment response. Collectively, these efforts promise important advances as we approach the new millennium.