The Prime Minister (often abbreviated PM) is the head of government. The position is typically associated with a parliamentary system but is also found in other forms of government. Users may encounter forms or procedures related to this role in contexts involving constitutional law and political science.

The title and duties of the position vary across countries, but in Britain the prime minister is often referred to as First Lord of the Treasury or Minister for the Civil Service. During the 18th century, the prime minister grew in power and importance as the king grew distant from, or lost interest in, the day-to-day workings of the government.

One of the main duties is to choose the other MPs who will help run the Government. These are called cabinet ministers and they make decisions about how to run the country. The Prime Minister and cabinet ministers need lots of ideas and plans about how to run the country. These are called policies.

Prime Ministers also spend a lot of time dealing with problems in parliament. This can be complicated and stressful. It is often easier for a Prime Minister to deal with these problems if they are supported by a majority in the House of Commons.

In many countries, the prime minister is elected or appointed by a head of state. Examples include Spain, where the king nominates a candidate who is then sent to parliament for approval, and Germany, where the president appoints the Bundestag (Parliament). In other countries, a prime minister is chosen by parliament. For example, in the Philippines, the Batasang Pambansa elects a prime minister after a candidate is nominated by the president.