PROJECT SUMMARY/ABSTRACT Parkinson’s disease (PD) is a progressive, neurodegenerative condition that impacts multiple sensorimotor systems. Swallowing disorders (dysphagia) occur frequently in PD and can devastatingly impact morbidity, mortality, and quality of life. As PD-centered medical and surgical approaches do not meaningfully impact dysphagia, behavioral rehabilitation is the standard of care for persons with PD-related dysphagia. However, it is unknown when and how swallowing function begins to decline in PD, prior to crossing the threshold into clinical dysphagia. This unclear understanding of dysphagia progression in PD leaves a critical gap in knowledge, forcing clinicians to wait to begin therapy until the patient complains of dysphagia, which may not occur until a point when significant neurodegeneration has occurred and lasting improvement in swallowing function may be unattainable. Several quantitative, objective, and sensitive techniques for measuring swallowing physiology have identified differences in function between healthy individuals and those with PD, but it is unknown how these measures of physiology change over time. In this study, we aim to identify measures that characterize progression of swallowing dysfunction in persons with Parkinson’s disease. This study proposes a cross-sequential, observational design to comprehensively assess swallowing physiology in a cross-sectional and longitudinal manner, paving the way for improved understanding of swallowing decline in PD and for a personalized medicine approach for dysphagia rehabilitation. Specifically, this study will allow for the collection of sufficient preliminary data and optimization of data collection and analysis protocols to support an NIH R01 application, with the overall objective to longitudinally follow patients, asses for dysphagia progression, and develop algorithms to predict risk for dysphagia development. Our central hypotheses are that 1) Pressure and mastication measures will exhibit greater amounts of change over time than imaging or respiratory measures; and 2) Rate of swallowing function change will be slower in early-stage PD compared to mid-stage PD. Optimization of comprehensive swallowing physiology assessment will lead to improvements in understanding of progression of swallowing deficits and potential for behavioral modification of swallowing in persons with PD. Improved characterization of swallowing decline will lead to more precise assessment and diagnosis of dysphagia, better targeting of windows of opportunity for swallowing rehabilitation, and more specific outcome measurements as the field explores novel treatment approaches.