The Urban Institute Health Policy Center's Medicaid/CHIP Eligibility Simulation Model is a microsimulation that uses rules about Medicaid/CHIP eligibility to approximate adults' and children's eligibility for Medicaid and CHIP. It has been used to simulate eligibility in the 50 states and Washington DC for the years 2008-2012 (before the Affordable Care Act [ACA] was implemented) and 2014 (simulating the new coverage provisions of the ACA). It has also been used to simulate eligibility in Puerto Rico in 2011 and enrollment under hypothetical statehood. It relies on the American Community Survey (ACS) and the Puerto Rico Community Survey (PRCS).