The Legislative Reference Bureau was created in 1913, the first of the modern legislative service agencies in Illinois. The Bureau carries out a wide range of functions relating to the legal and technical operation of the General Assembly. The primary task of the Bureau is the drafting and preparation of legislation, including bills, amendments, resolutions, and conference committee reports. The vast majority of all legislation considered by the General Assembly is drafted by the Bureau's staff, which in a typical biennium produces more than 31,000 documents. Attorneys employed by the Bureau provide legal advice and drafting services to legislators of each chamber, working on a nonpartisan basis in a confidential lawyer-client relationship. The Bureau's drafting staff also includes resolution drafters who draft resolutions and provide other drafting assistance.

For use in the drafting process, the Bureau maintains a computer database of the current Illinois statutes, which it continually updates and edits as new laws are passed. While the statute database is primarily designed for internal use, it also is available in electronic form on the General Assembly Web site.

The Bureau is responsible for recommending and preparing technical changes to the law. It prepares revisory bills that combine multiple enactments, correct typographical errors, and revise, renumber, and rearrange the law. The Bureau also prepares bills to codify selected portions of the law and to implement executive branch reorganizations ordered by the Governor.
In 1989, the Bureau began working on a plan for the reorganization of the Illinois statutes, and on January 1, 1993, the new Illinois Compiled Statutes became effective. The Bureau has a continuing duty to maintain the organization of the Illinois Compiled Statutes through periodic filings with the Secretary of State.

As an aid in tracking legislation, the Bureau prepares and publishes the Legislative Synopsis and Digest. The Digest contains a summary of legislative documents considered by the General Assembly, a record of all legislative actions on the documents, and several indices. The Digest is published in book form during most weeks that the General Assembly is in session and is available to the public by subscription. Digest summaries and actions for individual bills and resolutions are available via the General Assembly Web site.

After the end of each spring legislative session, the Bureau's legal staff reviews all reported decisions of the federal courts, the Illinois Supreme Court, and the Illinois Appellate Court from the previous year. Cases that affect the interpretation of the Illinois Constitution or statutes and cases that indicate a possible need for legislative action are identified and summarized in an annual Case Report, which is published by the Bureau.

The Bureau maintains a library, which includes an extensive collection of current and historical materials relating to Illinois statutes and legislative documents, other materials relating to the development and interpretation of Illinois law, and online resources relating to Illinois, federal, and other state legislation, laws, and court opinions.

The Bureau coordinates the activities of the Illinois delegation to the National Conference of Commissioners on Uniform State Laws.

The Bureau is governed by the Joint Committee on Legislative Support Services and the Legislative Reference Bureau Board, which is composed of the Secretary of the Senate, the Clerk of the House, the Assistant Clerk of the House, and the Assistant Secretary of the Senate.