Patellar instability is frequently seen in young patients. It can lead to significant morbidity and arthritis. Its management is controversial. JUPITER (Justifying Patellar Instability Treatment by Early Results)is a multi-center, multi-armed, prospective cohort study. Its specific aims are to compare the safety and efficacy of (1) non-operative treatment, (2) isolatedMedial Patellofemoral Ligament (MPFL) reconstruction, and (3) ‘à la carte’ surgical approach to treat patellar instability. Enrollment will take place for 3 years (2018 through 2020) at 12 sports centers. Outcomes would be assessed at 6 months, 1 year, 2 years, 5 years and 10 years, including assessment of function, activity level, quality of life and complications.