A Study in Subjects With Parkinson's Disease to Evaluate the Safety and Tolerability of Titration and Continuous Subcutaneous Infusion of ABBV-951 in an Outpatient Environment

* Subject with a diagnosis of definite idiopathic Parkinson's disease (PD) that is levodopa-responsive according to the United Kingdom Parkinson's Disease Society Brain Bank Criteria. * Subject must be taking an optimized and stable regimen of oral medications for PD, which has remained stable and unchanged for at least 30 days before enrollment in this study. * Subject is judged inadequately controlled on current therapy in the opinion of the Investigator and must experience a minimum of 2.5 hours of "off" time per day prior to Enrollment. * Subjects with a MMSE score greater than or equal to 24 and considered by the Investigator to not have dementia.

* Subjects with clinically significant electrocardiogram (ECG) values. * History of significant skin conditions or disorders that in the Investigator's opinion would interfere with the infusion of the study drug or could interfere with study assessments. * Receipt of an investigational product within at least 6 weeks prior to study drug administration. * Subjects with moderate to severe kidney disease. * Consideration by the investigator for any reason that the subject is an unsuitable candidate to receive ABBV-951. * Patient/caregiver that cannot demonstrate proper use of the devices (drug pump and wearable device) will not be allowed to participate.