Parkinson’s disease is believed to have a long prodromal period, consisting of early nonmotor symptoms and subtle motor signs. Reliable identification of individuals in this period is a focus of research along with the parallel discovery and implementation of biomarkers that reflect accumulating pathology and disease activity. A biomarker, as defined by the World Health Organization, is any substance, structure, or process that can be measured in the body or its products and influence or predict the incidence of an outcome or disease. This chapter covers the risk factors in Parkinson’s disease, symptoms that predate the diagnosis of Parkinson’s disease, and biomarkers for Parkinson’s disease. Biomarkers for Parkinson’s disease have been sought in various media including peripherally in blood, salivary glands, skin and colonic mucosa, and more centrally in cerebrospinal fluid (CSF). An important feature of candidate biomarkers should be their correlation with clinical features and progression of Parkinson’s disease pathology.