This chapter discusses the use of magnetic resonance spectroscopy (MRS) and functional magnetic resonance imaging (fMRI) techniques in childhood-onset anxiety disorders. It reviews brain imaging studies in various childhood-onset anxiety disorders, including obsessive-compulsive disorder (OCD), generalized anxiety disorder (GAD), panic disorder, social phobia, and post-traumatic stress disorder (PTSD), as well as suggest directions for future investigation. Functional neuroimaging has most consistently identified the caudate nucleus, ventral prefrontal cortex, and anterior cingulate as neural substrates of OCD. These regions have shown abnormal serotonergic and/or glutamatergic function. The brain regions implicated in panic disorder are consistent with the brain networks subserving fear and anxiety. The structural imaging findings suggest that functional dysfunction in the hippocampus is associated with PTSD. The studies highlight that some of the common findings in OCD and PTSD may reflect similarities in symptoms, with both disorders involving repetitive, ritualistic behaviors and intrusive thoughts.