The semi-presidential system is a system of government that features both a prime minister and a president who are active participants in the day to day functioning of government. It differs from the parliamentary system in that it has a popularly elected president who is not a ceremonial figurehead and it differs from the presidential system in that it has an executive prime minister who has some responsibility to the legislature.

How the powers between president and prime minister are divided can vary greatly between countries. For example, in France the president is responsible for foreign policy and the prime minister for domestic policy. In this case, the division of power between the prime minister and the president is not explicitly stated in the constitution, but has evolved as a political convention. In contrast, while Finland employs a system effectively copied from France, this division of power is explicitly stated in the constitution: "the foreign policy is led by the president in cooperation with the cabinet".

Semi-presidential systems are sometimes typified by periods of cohabitation, in which the prime minister and president are elected separately, and often from rival parties. This can create an effective system of checks and balances or a period of bitter and tense stonewalling, depending on the attitudes of the two leaders, the ideologies of their parties, or the demands of their constituencies. As a typical example, Sri Lankan politics for several years witnessed a bitter struggle between the President and the Prime Minister, belonging to different parties and elected separately, over the negotiations with the LTTE to resolve the longstanding ethnic conflict.

Some current nations that feature semi-presidential systems include:

• Algeria
• Egypt (supposedly; Egypt is in fact an authoritarian state and while both President and Prime Minister have a great deal of power, the President, as a rule, can more or less choose the Prime Minister as he pleases)
• Finland
• France
• Lebanon
• Lithuania
• Mongolia
• Pakistan (since 1998, supposedly; Pakistan is in fact a military dictatorship ruled almost exclusively by General Pervez Musharraf)
• Romania
• Russia
• Sri Lanka
• Ukraine
• Taiwan (Republic of China)

Interestingly, some nations that are classified as parliamentary, such as Austria and Ireland actually have constitutions that give their presidents more power than the President of France has. By tradition, presidents in Austria and Ireland do not use their powers, and those nations do not function in a semi-presidential way. Furthermore, in Finland, the new constitution of 2000, which combined the previous four constitutional laws, limited the power of the president. Some powers that the president could previously use unilaterally require, under the 2000 constitution, the co-operation of the parliament and the government; this makes it difficult to classify Finland under the semi-presidential or parliamentary category.

States that featured semi-presidential systems include:

• Germany from 1919-1933 (officially until 1949)
• Croatia from 1990-2000.

Sistema semi-presidencialista | Semipräsidentielles Regierungssystem | República semipresidencialista | 이원집정부제 | Repubblica semipresidenziale | 半大統領制 | Semipresidentialisme | Смешанная республика | 半总统制