The Leader of the Opposition is a title traditionally held by the leader of the largest political party not in government, typical in countries utilizing the parliamentary system form of government. The leader of the opposition is typically seen as an alternative prime minister, premier, first minister, or chief minister to the incumbent; in the Westminster system, they head a rival alternative government known as the shadow cabinet or opposition front bench. The same term is also used to refer to the leader of the largest political party that is not in government in subnational state, provincial, and other regional and local legislatures.

This article does not cite any sources. (December 2009)

In many Commonwealth realms, the full title for the Leader of the Opposition is the Leader of His Majesty's Most Loyal Opposition.

• Leader of the Opposition (Northern Ireland)
• Leader of the Opposition (Rhodesia)

• Minority leader, for a similar role in countries utilizing the presidential system
• Parliamentary opposition
• Shadow cabinet