The U.S. Government is the world's largest publisher producing information on every subject from accounting to zoology. Government documents are excellent primary sources for documenting U.S. history and this includes state and local government documents as well as those from the federal government. Purdue Libraries are a depository for U.S. Government Documents and provide extensive access to government documents from the 1950s. U.S. Government documents are classified using the Superintendent of Documents (SuDoc) classification which arranges these documents alphabetically by the agency producing them.