Real-World Study of ABBV-951 Subcutaneous Infusion to Assess Change in Disease Activity in Adult Participants With Parkinson's Disease

Inclusion Criteria: * Eligibility for ABBV-951 therapy in accordance with the approved local label in the participating country and local reimbursement regulations, if applicable. * Diagnosis of levodopa-responsive idiopathic Parkinson's Disease (PD). * Participant must be either: * Cohort A: Naïve to ABBV-951 * Cohort B: Pre-treated with ABBV-951, specifically, participants of Open-Label Extension Studies M15-737 and M20-098 who completed these studies without significant protocol deviations and who did not experience an adverse event (AE) that in the investigator's opinion may indicate an unacceptable safety risk. * Decision to treat with ABBV-951 (or continue the treatment in Cohort B) made by the clinician prior to any decision to approach the participant to participate in this study. * Prior to any study-related procedures being performed, the participant, or legal authorized representative (LAR) has voluntarily signed an Authorization for Use/Disclosure of Data (AUDD)/informed consent form (ICF) according to national regulations after the study has been explained and the participant has had the opportunity to have questions answered. Exclusion Criteria: * Any condition included in the contraindications section of the approved local ABBV-951 label in the participating country. * Mini-Mental State Examination (MMSE) score \< 24. * If the participant has a score of 19-23, he/she can be included if based on the investigator´s judgment the participant is able to handle the therapy and follow the study procedures with the help of a permanent caregiver. * Participation in a concurrent interventional clinical trial from enrollment and throughout the study. * History of significant skin conditions or disorders per investigator´s judgment. In case of temporary affections like recent sunburn, acne, scar tissue, tattoo, open wound, branding, or colorations, the participant should not be included if the investigator considers these as interfering with the infusion of study drug or with study assessments.