The differences between a president and a prime minister largely depend on the countries to which one is referring. A country might have one or the other — or even both — and their powers can vary depending on the type of government that a country has and the specific laws that apply to its government. Some are heads of state, and others are merely heads of government, which means that they lead the operations of their governments but are not as powerful as heads of state. In general, a president typically is elected by the people and is separate from the country's legislative body, and a prime minister typically is a member of the legislative body who is chosen by that legislature to be its leader.
In a parliamentary government, the prime minister often is appointed by the parliament. The appointment will almost always be made by the party that has the most members of parliament. In this way, citizens who vote for parliamentary members indirectly influence the choice of prime minister, because a high number of parliamentary members from the same party will elect a prime minister from that party. The prime minister leads the parliament and therefore is the head of government but usually is not the head of state — a monarch, president or other official typically has that role. In some countries, such as the United Kingdom, the prime minister is appointed by a monarch, usually at the recommendation of the party that controls parliament.
Many times, the prime minister is the leader of the legislature but also must answer to the legislature and could even be ousted by it. He or she often must appear before the legislature on a regular basis, such as once a week, and answer questions regarding his or her decisions. If the legislature doesn’t like the answers, the members could decide to elect a new prime minister. Some countries also require an election for the prime minister at certain intervals, such as every five years, as in the U.K.
A president usually does not have to answer to the country's legislative body except in certain circumstances, such as when he or she is accused of an illegal act, such as abusing his or her power. He or she might make speeches to the legislature and might take questions, but he or she is not required by law to defend his or her decisions in front of the legislature. Also, the president is elected by the people separately from the legislature, so he or she might be from a political party that is different from the party that controls the legislature.
In some countries, such as France, the president is elected by the people and must appoint a prime minister. Thus, the prime minister is likely to be from the president’s political party. The prime minister in a country that also has a president typically has less power to act than a prime minister in a country whose head of state is mostly a figurehead. Sometimes, a monarch or the ruling family chooses the country's prime minister. When this is the case, the appointee usually acts in concert with the wishes of the country’s ruler or rulers and might ensure that those wishes are carried out by the government.