A shadow cabinet is a sort of government in (electoral) exile, as a powerless but influential "shadow" of the actual executive branch aligned with and appointed by one or more parties currently out of power. The shadow cabinet parallels the actual cabinet, consisting of figures who would be appointed as the heads of major ministries, departments, or the like if the opposition were in fact in control of the government. Though they wield no actual power, the members of a shadow cabinet can use media and public attention to disseminate their party line, influence the political process, and position their parties for future dominance.

Shadow cabinets are more common in parliamentary republics like those predominant in Europe than in divided-power presidential governments along the U.S. model. When control of the legislature produces control of the executive, parties other than the ruling party or coalition are often effectively powerless, and face the possibility of being unable to check their opponents' initiatives, or even to shape the legislative agenda. Meanwhile, in addition to the opportunity to put their plans into action, the parties in power are able to reap the political benefits of incumbency as they dominate the nation's political discourse and mindshare, taking full credit for government successes (though, in fairness, they risk suffering full blame for its failures).

A shadow government, by existing in the public eye and periodically issuing statements representing the policies it would apply to the issues of the day, allows the opposition party to introduce new terms and proposals to the debate, influencing the government's course of action, and maintains an image of the opposition as unified, vital, and productive, rather than simply rolling over in the face of their rivals' dominance. In addition, as there is always the potential for a vote of no confidence to radically restructure the government, it may prove useful for the opposition to maintain a government-in-waiting for just such an occasion. The existence of a shadow government can even, by presenting a clear alternative to the standing government, with appointees chosen to appeal to selected constituencies, increase the likelihood of such a government turnover by winning over the support of legislators for such a vote of no confidence and/or voters for the next general election.