An unholy alliance is a coalition among seemingly antagonistic groups for ad hoc or hidden gain, generally some influential non-governmental group forming ties with political parties, supplying funding in exchange for the favorable treatment. Like patronage, unholy alliances are not necessarily illegal, but unlike patronage, by its deceptive nature and often great financial resources, an unholy alliance can be much more dangerous to the public interest. An early use of the term was by former US President Theodore "Teddy" Roosevelt:

When groups that are antagonistic to each other form a coalition for hidden gain, it is called what?