Many studies examine the anti-poverty effects of social insurance and means-tested transfers, relying solely on survey data with substantial errors. We improve on past work by linking administrative data from Social Security and five large means-tested transfers (SSI, SNAP, Public Assistance, the EITC, and housing assistance) to 2008-2013 Survey of Income and Program Participation data. Using the linked data, we find that Social Security cuts the poverty rate by a third – more than twice the combined effect of the five means-tested transfers.