A cabinet reshuffle or shuffle is when a head of government rotates or changes the composition of ministers in their cabinet. They are more common in parliamentary systems, than in other democratic systems where cabinet heads must be confirmed by a separate legislative body, and occur at pleasure in autocratic systems without suitable checks-and-balances.
Cabinet reshuffles happen in parliamentary systems for a variety of reasons. Periodically, smaller reshuffles are needed to replace ministers who have resigned, retired or died. Reshuffles are also a way for a premier to "refresh" the government, often in the face of poor polling numbers; remove poor performers; and reward supporters and punish others. 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 from the retirement or defeat of individual ministers at the election. Similarly, when a new prime minister enters office from the same party as the previous one, he or she might appoint a very different ministry than that of his or her predecessor to reflect a change in policies and priorities; an example is Gordon Brown's government, formed on 28 June 2007 after the departure of Tony Blair the previous day.
A reshuffle also provides an opportunity to create, abolish and rename departments (and ministerial posts) and to reassign responsibilities among departments. This may be done to reflect new priorities or for reasons of efficiency.
Cabinet reshuffles 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 members to 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 multiple cabinet secretaries to new positions, especially since a United States Cabinet member moved to a new position within the cabinet needs to be confirmed in the new role by the United States Senate--this alone is seen as a powerful deterrent against U.S. presidents initiating major cabinet reshuffles. On an individual basis, however, U.S. Cabinet members will occasionally change departments--for example, Norman Mineta served as Secretary of Commerce under Bill Clinton before becoming Secretary of Transportation for Clinton's successor, George W. Bush.