This document is a reference guide to the data the Census Bureau provides to states and other jurisdictions for their redistricting efforts. Note that this guide focuses on the redistricting process and not the apportionment process. Additionally, this guide focuses on the time following the mid-1960s when a series of U.S. Supreme Court decisions fundamentally changed the redistricting process. These changes to the redistricting process imposed new data needs on the states and led to the enactment of P.L. 94-171.