The Federal Register is the official daily publication of the federal government's proposed, interim, and final rules; Presidential Documents and Executive Orders; and notices (documents other than rules that are applicable to the public). The Federal Register has been printed daily (Monday to Friday) since 1936.
A basic citation to a rule in the Federal Register using Bluebook* citation style is as follows:
Authorization of Representative Fees, 74 Fed. Reg. 48381 (Sept. 23, 2009) (amending 20 C.F.R. § 404.1720).
The citation tells you that the title of the rule is "Authorization of Representative Fees." It can be found in volume 74, page 48381 of the Federal Register issued for September 23, 2009. The second parenthetical tells you that the rule will amend Title 20, Section 404.1720, of the Code of Federal Regulations.
* The rules governing the most widely used legal citation style are found in The Bluebook: A Uniform System of Citation.
Several sites offer free access to the Federal Register online.
Several subscription legal research databases offer access to a full run of the Federal Register (1936-present). The following subscription databases (marked with a padlock ) are available onsite at the Library of Congress: