Chapter 7 examines current knowledge concerning panic disorder (PD) and obsessive-compulsive disorder (OCD). Background information is reviewed along with comorbidity and multicultural findings. Etiologic theories are reviewed including research findings from heritability, family, and twin studies along with linkage and genomewide association studies. Specific candidate genes putatively involved in PD and OCD are discussed. Structural studies are reviewed concerning anatomical brain findings along with functional neuroimaging findings. Results from neurotransmitter studies are also reviewed concerning PO and bipolar disorder. Several brain-based models of anxiety are presented. The use of pharmacological interventions and specific medications are discussed, as well as the mode of action of these medications. Lastly, the use of neurosurgery and brain stimulation techniques in the treatment of OCD is reviewed.