In the parliamentary system a cabinet shuffle or reshuffle is an informal term for an event that occurs when a head of government rotates or changes the composition of ministers in their cabinet.
Commonly, a cabinet shuffle refers to certain ministers being shifted from one portfolio to another. Cabinet shuffles happen periodically as moving ministers is often necessary to replace ministers who have resigned or retired. Forming cabinets is also one of the most important ways for a head of government to reward or punish supporters, a practice that leads to shuffles whenever a new faction within a party takes over. It is common after elections, even if the party in power is retained, as the prime minister's reading of public opinion as evidenced by the election may require some change in policy, in addition to any changes resulting in the retirement and (occasionally) outright electoral defeat of some former ministers. Furthermore, when a new prime minister enters office from the same party as the previous one, he or she might not re-appoint all of the same Cabinet Ministers as the previous leader had appointed, preferring to reflect his or her own policies; an example is Gordon Brown's government, formed in 2007 after the departure of Tony Blair.
Cabinet shuffles are far less common in systems where members of the Cabinet are not drawn from the legislative branch. In such systems, there is a far larger pool of viable candidates to choose a cabinet from. Members of such cabinets are usually chosen on account of their qualifications to run a specific portfolio, so moving these cabinet member different portfolios at a later time usually makes little sense. For instance, in the United States, it would be very unusual for a president to reassign all the cabinet secretaries to new positions, especially since a United States Cabinet member moved to a new position needs to be confirmed in the new portfolio by the United States Senate - this alone is seen as a powerful deterrent against U.S. presidents initiating major cabinet shuffles. On an individual basis however, United States Cabinet members will occasionally change portfolios - for example, Norman Mineta previously served as Secretary of Commerce before being moved to Secretary of Transportation.