PURPOSE: Improving primary care quality is a national priority, but little is known about the extent to which small to medium-size practices use quality improvement (QI) strategies to improve care. We examined variations in use of QI strategies among 1,181 small to medium-size primary care practices engaged in a national initiative spanning 12 US states to improve quality of care for heart health and assessed factors associated with those variations. METHODS: In this cross-sectional study, practice characteristics were assessed by surveying practice leaders. Practice use of QI strategies was measured by the validated Change Process Capability Questionnaire (CPCQ) Strategies Scale (scores range from -28 to 28, with higher scores indicating more use of QI strategies). Multivariable linear regression was used to examine the association between practice characteristics and the CPCQ strategies score. RESULTS: The mean CPCQ strategies score was 9.1 (SD = 12.2). Practices that participated in accountable care organizations and those that had someone in the practice to configure clinical quality reports from electronic health records (EHRs), had produced quality reports, or had discussed clinical quality data during meetings had higher CPCQ strategies scores. Health system-owned practices and those experiencing major disruptive changes, such as implementing a new EHR system or clinician turnover, had lower CPCQ strategies scores. CONCLUSION: There is substantial variation in the use of QI strategies among small to medium-size primary care practices across 12 US states. Findings suggest that practices may need external support to strengthen their ability to do QI and to be prepared for new payment and delivery models.