In this handbook, the U.S. Census Bureau’s Disclosure Avoidance System is described in the context of the 2020 Census Redistricting Data (P.L. 94-171) Summary File because those are the first 2020 Census data protected using the new confidentiality procedures. The apportionment counts released earlier, in April 2021, were not subject to these new confidentiality procedures and were the actual enumerated population counts for each state.