Bid rigging is a form of fraud in which a commercial contract is promised to one party even though for the sake of appearance several other parties also present a bid. This form of collusion is illegal in most countries. It is a form of price fixing and market allocation, often practiced where contracts are determined by a call for bids, for example in the case of government construction contracts.

Bid rigging almost always results in economic harm to the agency which is seeking the bids, and to the public, who ultimately bear the costs as taxpayers or consumers.

There are some very common bid rigging practices:

These forms of bid rigging are not mutually exclusive of one another, and two or more of these practices could occur at the same time. For example, if one member of the bidding ring is designated to win a particular contract, that bidder's conspirators could avoid winning either by not bidding ("bid suppression"), or by submitting a high bid ("cover bidding").

In the United States, bid rigging is a criminal offense under Section 1 of the Sherman Act. In Canada, it is a criminal offense under Section 47 of the Competition Act.