From January through December 2015, the California Department of Health Care Services, which administers Medi-Cal, the nation's largest Medicaid program, conducted a quality improvement collaborative (QIC) with 9 Medi-Cal managed care plans (MCPs) aimed at improving hypertension control consistent with the Million Hearts initiative. The QIC included quarterly webinars and links to local, state, and national resources that consisted of materials and consultations with subject matter experts. Participating MCPs demonstrated an average increase of 5.0 percentage points in their rates of controlled hypertension. Collaboratives can achieve substantial quality improvement in Medicaid managed care plans.