The Parkinson's Progression Markers Initiative (PPMI) is a landmark clinical study aiming to identify biomarkers of Parkinson's disease progression. The discovery of a Parkinson's biomarker is critical to developing treatments that can go beyond symptomatic relief to slow or stop the progression of Parkinson's disease. PPMI needs 400 newly diagnosed Parkinson's patients who have not yet begun medication and 200 control participants who do not have Parkinson's disease or a close relative with Parkinson's.