In some countries, particularly those under the Westminster system, the Cabinet collectively decides the government's policy and tactical direction, especially in regard to legislation passed by the parliament. In countries with a presidential system, such as the United States, the cabinet does not function as a collective legislative influence; rather, their primary role is as an unofficial advisory council to the head of government, consisting of the heads of the executive departments they are appointed to lead. Instead of just one view, the president gets opinions and advice in upcoming decisions. In some countries, cabinets are required to be appointed from sitting members of the legislature while in others, such as the United States, cabinet members may not be sitting legislators; they must resign their legislative office if they accept a cabinet appointment.
In most governments, members of the cabinet are given the title of minister, and each holds a different portfolio of government duties ("Minister for the Environment", etc). In a few governments, as in the case of the United States, the Philippines and the United Kingdom, the title of secretary is also used for some cabinet members ("Secretary of Education", etc). The day-to-day role of most cabinet members is to serve as the head of one segment of the national bureaucracy, as the head civil servant to which all other employees in that department report.
The size of cabinets varies, although most contain around ten to twenty ministers. Researchers have found an inverse correlation between a country's level of development and cabinet size: on average, the more developed a country is, the smaller is its cabinet.
Under the Westminster system, members of the cabinet are collectively responsible for all government policy. All ministers, whether senior and in the cabinet or junior ministers, must publicly support the policy of the government, regardless of any private reservations. Although, in theory, all cabinet decisions are taken collectively by the cabinet, in practice many decisions are delegated to the various sub-committees of the cabinet, which report to the full cabinet on their findings and recommendations. As these recommendations have already been agreed upon by those in the cabinet who hold affected ministerial portfolios, the recommendations are usually agreed to by the full cabinet with little further discussion.
Cabinet deliberations are secret and documents dealt with in cabinet are confidential. Most of the documentation associated with cabinet deliberations will only be publicly released a considerable period after the particular cabinet disbands; for example, thirty years after they were discussed.
In theory the prime minister/premier is first among equals. However, the prime minister is the person whom the monarch or president will ultimately take advice from on the exercise of executive power, which may include the powers to declare war, use nuclear weapons, expel ministers from the cabinet, and to determine their portfolios in a cabinet reshuffle. This position in relation to the executive power means that, in practice, the prime minister has a high degree of control over the cabinet: any spreading of responsibility for the overall direction of the government has usually been done as a matter of preference by the prime minister – either because they are unpopular with their backbenchers, or because they believe that the cabinet should collectively decide things.
The shadow cabinet consists of the leading members, or frontbenchers, of an opposition party, who generally hold critic portfolios "shadowing" cabinet ministers, questioning their decisions and proposing policy alternatives.
The Westminster cabinet system is the foundation of cabinets as they are known at the federal and state (or provincial) jurisdictions of Canada, Australia, New Zealand, India, and other Commonwealth of Nations countries whose parliamentary model is closely based on that of the United Kingdom.
Under the doctrine of separation of powers, a cabinet under a presidential system of government is part of the executive branch. In theory, at least, they carry out policy rather than create it. In addition to administering his or her segment of the executive branch, a cabinet member is responsible for advising the head of government on areas within his or her purview. They are appointed by and serve at the pleasure of the head of government; they are strongly subordinate to the executive and can be replaced at any time. Normally, since they are appointed by the executive, they are members of the same political party, but the executive is free to select anyone, including opposition party members, subject to Congressional confirmation.
Normally, the legislature or a segment thereof must confirm the appointment of a cabinet member; this is but one of the many checks and balances built into a presidential system. The legislature may also remove a cabinet member through a usually difficult impeachment process.
In the United States Cabinet, cabinet members do not serve to influence legislative policy to the degree found in a Westminster system; however, each member wields significant influence in matters relating to their executive department. Since the administration of Franklin Roosevelt, the President of the United States has acted most often through his own executive offices or the National Security Council rather than through the cabinet as was the case in earlier U.S. administrations.