An omnibus bill is a proposed law that covers a number of diverse or unrelated topics. Omnibus is derived from Latin and means "for everything". An omnibus bill is a single document that is accepted in a single vote by a legislature but packages together several measures into one or combines diverse subjects.
Because of their large size and scope, omnibus bills limit opportunities for debate and scrutiny. Historically, omnibus bills have sometimes been used to pass controversial amendments. For this reason, some consider omnibus bills to be anti-democratic. 
In the United States, examples include reconciliation bills, combined appropriations bills, and private relief and claims bills.
Omnibus legislation is routinely used by the United States Congress to group together the budgets of all departments in one year in an omnibus spending bill. For example, the Omnibus Budget Reconciliation Act of 1993 was designed to help reduce the federal deficit by approximately $496 billion over five years through restructuring of the tax code. 
During the 19th century, there were three notable omnibus bills.
The Compromise of 1850 had five disparate provisions designed by Sen. Henry Clay of Kentucky. His purpose was to pacify sectional differences that threatened to provoke the secession of the slave states. The Fugitive Slave Act was the most infamous of the five compromise components, and was almost universally excoriated by abolitionists, the chief exception being Sen. Daniel Webster of Massachusetts who prioritized preservation of the Union. Sen. Thomas Hart Benton, a Missouri slaveholder, opposed the omnibus compromise as an "unmanageable mass of incongruous bills, each an impediment to the other...."  Nonetheless, the bill passed Congress and accomplished its purpose. Disunion and civil war were delayed for a decade.
The Omnibus Act of February 22, 1889, provided for the admission of four new states to the Union — North Dakota, South Dakota, Montana and Washington.
In Canada one famous omnibus bill became the Criminal Law Amendment Act, 1968-69, a 126-page, 120-clause amendment to the Criminal Code, which dealt with issues as diverse as homosexuality, prostitution, abortion, gambling, gun control and drunk driving. Likewise, Jobs and Growth Act (2012). In the Republic of Ireland, the Second Amendment of the Constitution was an omnibus constitutional law, enacted in 1941, that made many unrelated changes to the country's fundamental law.
Section 55 of the Constitution of Australia requires that laws imposing taxation "deal only with the imposition of taxation" and "deal with one subject of taxation only" (except those relating to customs and excise); other purported provisions in a piece of tax legislation are of no legal effect. This does not outlaw all omnibus bills, but renders unconstitutional any omnibus bill imposing taxation. 
- "Omnibus bills in Hill history". Lorne Gunter. Sun Media. 18 June 2012. Retrieved 18 June 2013.
- "Omnibus act 1993". Real Estate Agent.
- John F. Kennedy, Profiles in Courage (1956), chapter IV.
- Arkansas (on June 22, 1868), Alabama, Florida, Georgia, Louisiana, North Carolina, South Carolina (on June 25, 1868).
- "Govt to limit Labour position on TPP bill". Patrick O'Meara, Economics Correspondent. RNZ. 5 Feb 2016. Retrieved 7 Feb 2015.
- "New Zealand: Trans-Pacific Partnership Bill Passed". 22 November 2016.
- Constitution of Australia, s. 55