The Affordable Care Act is the most fundamental legislative transformation of the US health care system in forty years. This analysis estimates that the act will provide health insurance for an additional 3.4 million people in California in 2016. This will mean that nearly 96 percent of documented residents of California under age sixty-five will be insured. Enrollment in Medi-Cal, the state’s Medicaid program, is expected to increase by 1.7 million people, while 4.0 million people are expected to enroll in the state’s planned new health insurance exchange. Employer-sponsored insurance and spending on health insurance will decline slightly. Low-income households will experience substantial financial benefits, but families at the highest income levels will pay more.