Dr. Lang has been involved in research related to Parkinson disease and other movement disorders for over 40 years. A great deal of his research involves the study of multiple facets of Parkinson disease and related movement disorders with particular focus on attempting to define disease etiology and pathogenesis, better establish natural history and more definitive diagnostic assessments, and develop effective disease-modifying and symptomatic therapies. In recent years, he has been involved in efforts to redefine Parkinson disease acknowledging the prolonged prodromal period. He has collaborated in formal calls to the field emphasizing the need to redefine the disorder and he has actively participated in the International Parkinson and Movement Disorder Society’s efforts to create new diagnostic criteria for Parkinson disease as well as to propose research criteria for prodromal disease. He has also been involved in the study of the 4-repeat tauopathies, Progressive Supranulear Palsy (PSP) and Corticobasal Degeneration (CBD). He was one of the senior authors developing diagnostic criteria for CBD and he has been a member of the MDS PSP Study Group that has published new proposed diagnostic criteria for PSP. Both of these efforts acknowledged the phenotypic variability of these disorders and the need to be able to make early accurate clinical diagnoses so that patients can be enrolled in future disease-modifying therapeutic trials (e.g., with tau vaccines).