The central role of dopamine neuronal loss in Parkinson's disease provides a clear pathologic framework and rationale for imaging the system both to interrogate dynamic pathophysiologic changes as well as to aid in diagnosis and clinical management. Recent post mortem studies of Parkinson's brain provide a much fuller depiction of the inexorable and progressive topology of pathophysiologic changes, including brain alpha-synuclein deposition. This informs PET and SPECT evaluations for testing hypotheses regarding the course of degeneration in longitudinal studies of Parkinson's disease patients. Recent work has underscored the subtlety of change in the dopaminergic neuronal system and its neural connections as a function of disease status and treatment. The interplay between other neurochemical brain systems and dopamine elucidates potential new targets for therapeutic intervention across the stages of the disease.