Parkinson's disease (PD) is a chronic neurodegenerative disease that involves the selective loss of dopaminergic neuronal cells in the substantia nigra (SN) in the midbrain. The studies in PD-affected individuals as well as animal, cellular and toxicant-based disease models have provided information about the mechanisms involved in PD etiology. Intracellular signaling pathways offer a mechanistic explanation for how an initial event may induce selective cell death in PD and also specific targets for therapeutic intervention in PD.