The diagnosis and treatment of people with Parkinson’s disease (PD) and related conditions is based on the history and examination of the individual. Structured interviews and examinations facilitate the categorization of individuals by severity and group (PD, atypical parkinsonism, other neuropsychiatric disorders). Observation of individuals live and on video are used to monitor the course of patients. Instrumentation is developed to precisely quantify and categorize the atypicalities of motion in people with PD. Novel tools are proposed to record and interpret the motions and behaviors of persons with PD and related disorders. Potential biomarkers for PD and related conditions are proposed.