Mutations in parkin are the second most common known cause of Parkinson's disease (PD). Parkin is an ubiquitin E3 ligase that monoubiquitinates and polyubiquitinates proteins to regulate a variety of cellular processes. Loss of parkin's E3 ligase activity is thought to play a pathogenic role in both inherited and sporadic PD. Here, we review parkin biology and pathobiology and its role in the pathogenesis of PD.