By law, the US Government Publishing Office is the "official, digital, and secure source for producing, protecting, preserving, and distributing the official publications and information products of the federal government'" making it the world's largest publisher. To help locate and provide access to its vast output, "GPO aims to provide a comprehensive index of every document issued or published by a department, bureau, or office not confidential in character."
Most GPO publications have been published online since the late 1990s (and are listed in our library's Discovery service), and there has been extensive digitization of older documents by government agencies, by commercial database vendors (Voxgov, HeinOnline, ProQuest, Readex), and by nonprofits (LLMC-Digital, HathiTrust, Internet Archive, universities).
For most of a century, Virginia Tech automatically received most GPO output in print "docs," identified by GPO's unique "SuDoc" call number system. Knowing the SuDoc number of an older federal publication can be crucial for getting your hands on government publications in our collection or via ILLiad. Records in the GPO catalog (see below), GovInfo,gov, and Voxgov will provide SuDoc class numbers. It's common for an online version of government publication series to have the same basic SuDoc number as its first print issue. Don't be reluctant to ask a librarian for help crossing that print-online divide.