He signed into law the Patient Protection Affordable Care Act, which expands Medicaid coverage, prohibits insurance companies from denying care based on pre-existing illnesses, and supports medical research. There is a four-year window on the implementation of many of the law’s major measures.

“[The] bill I’m signing will set in motion reforms that generations of Americans have fought for and marched for and hungered to see,” Obama said upon signing the measure into law. “It will take four years to implement fully many of these reforms, because we need to implement them responsibly.”