This usually involves formal agreements between two or more entire parties.
A political group is usually especially beneficial to the parties concerned during and immediately after elections – due to characteristics of the electoral systems concerned (e.g. allowing each party to clear electoral thresholds) and/or allowing parties to participate in the formation of a government after elections.
These may break up quickly or hold together for decades, becoming the de facto norm, operating almost as a single unit.
[1] Coalition governments are formed when a political group comes to power or when only a plurality (not a majority) has been reached, and several parties must work together to govern.
One of the peculiarities of such a method of governance results in a minister without portfolio.