This article presents the MDS ( Movement Disorders Society ) criteria for diagnosing prodromal Parkinson's disease ( PD ), which refers to the early stages of the disease where neurodegeneration has begun but classic clinical symptoms are not yet fully developed. The criteria are designed for research purposes due to the lack of clear neuroprotective or disease-modifying therapies for prodromal PD. The methodology involves using a Bayesian classifier to calculate the probability of prodromal PD based on age-adjusted prevalence and likelihood ratios ( LRs ) of various diagnostic markers. These markers include motor and nonmotor clinical symptoms, signs, and ancillary tests. The criteria are intended to be updated continuously as new data become available. Key aspects of the criteria include the estimation of prior probability, calculation of LRs for risk and marker factors, and the combination of these factors to determine the final probability of prodromal PD. Ethical considerations and limitations of the criteria are also discussed, emphasizing the need for caution in disclosing prodromal disease status to patients.This article presents the MDS ( Movement Disorders Society ) criteria for diagnosing prodromal Parkinson's disease ( PD ), which refers to the early stages of the disease where neurodegeneration has begun but classic clinical symptoms are not yet fully developed. The criteria are designed for research purposes due to the lack of clear neuroprotective or disease-modifying therapies for prodromal PD. The methodology involves using a Bayesian classifier to calculate the probability of prodromal PD based on age-adjusted prevalence and likelihood ratios ( LRs ) of various diagnostic markers. These markers include motor and nonmotor clinical symptoms, signs, and ancillary tests. The criteria are intended to be updated continuously as new data become available. Key aspects of the criteria include the estimation of prior probability, calculation of LRs for risk and marker factors, and the combination of these factors to determine the final probability of prodromal PD. Ethical considerations and limitations of the criteria are also discussed, emphasizing the need for caution in disclosing prodromal disease status to patients.