This chapter presents studies of depression that use structural and functional imaging to examine the roles of different brain circuits and neurochemicals in the pathophysiology and treatment of the illness. Functional imaging studies have demonstrated changes in metabolism in the prefrontal cortex, anterior cingulate and amygdala in depression, and these findings are at least in part reversed with antidepressant treatment and cognitive behavioural therapy. Brain imaging in major depressive disorder has contributed to a better understanding of the pathophysiology of the illness from a neural system perspective as well as at the synaptic level. A recent meta-analysis of magnetic resonance imaging (MRI) studies in schizophrenia found that the most significant changes occur within the medial temporal lobe. The chapter also discusses neuroimaging in Alzheimer's disorder within the context of an emergent public health crisis concerning an illness with a relatively well-characterised histopathology.