Objective To investigate the potential spillover effects of the Hospital Readmissions Reduction Program (HRRP) on readmissions for nontargeted conditions and patient populations. We examine HRRP effects on nontargeted conditions separately and on non‐Medicare populations in Florida and California. Data Sources From 2007–2013, 100 percent Medicare inpatient claims data, 2007–2013 State Inpatient Database (SID) for Florida, and 2007–2011 SID for California. Study Design We conducted an interrupted time series analysis to estimate the change in 30‐day all‐cause unplanned readmission trends after the start of HRRP using logistic regression. Principal Findings Hospitals with the largest reductions in targeted Medicare readmissions experienced higher reductions in nontargeted Medicare readmissions. Among nontargeted conditions, reductions were higher for neurology and surgery conditions than for the cardiovascular and cardiorespiratory conditions, which are clinically similar to the targeted conditions. For non‐Medicare patients, readmission trends for targeted conditions in Florida and California did not change after HRRP. Conclusions Our findings are consistent with positive spillover benefits associated with HRRP. The extent of these benefits, however, varies across condition and patient groups. The observed patterns suggest a complex response, including a role of nonfinancial factors, in driving lower readmissions.