A parliamentary system, also known as parliamentarianism (and parliamentarism in U.S. English), is distinguished by the executive branch of government being dependent on the direct or indirect support of the parliament, often expressed through a vote of confidence. Hence, there is no clear-cut separation of powers between the executive and legislative branches, leading to a differing set of checks and balances compared to those found in a presidential republic. Parliamentary systems usually have a clear differentiation between the head of government and the head of state, with the head of government being the prime minister or premier, and the head of state often being an elected (either popularly or through parliament) president or hereditary monarch. Though in Parliamentary systems the prime minister and cabinet will exercise executive power on a day-to-day basis, actual authority will usually be bestowed in the head of state, giving them many codified or uncodified reserve powers, providing some balance to these systems.
The term parliamentary system does not mean that a country is ruled by different parties in coalition with each other. Such multi-party arrangements are usually the product of an electoral system known as proportional representation. Parliamentary countries that use first past the post voting usually have governments composed of one party. However, parliamentary systems in continental Europe do use proportional representation, and tend to produce election results in which no single party has a majority of seats.
Parliamentarianism may also be heeded for governance in local governments. An example is the city of Oslo, which has an executive council as a part of the parliamentary system. The council-manager system of municipal government used in some U.S. cities bears many similarities to a parliamentary system.

Types
Some believe that it's easier to pass legislation within a parliamentary system. This is because the executive branch is dependent upon the direct or indirect support of the legislative branch and often includes members of the legislature. In a presidential system, the executive is often chosen independently from the legislature. If the executive and legislature in such a system include members entirely or predominantly from different political parties, then stalemate can occur. Former US President Bill Clinton often faced problems in this regard, since the Republicans controlled Congress for much of his tenure. That being said, presidents can also face problems from their own parties, as former US President Jimmy Carter often did

Advantages of a parliamentary system
One main criticism of many parliamentary systems is that the head of government is in almost all cases not directly elected. In a presidential system, the president is usually chosen directly by the electorate, or by a set of electors directly chosen by the people, separate from the legislature. However, in a parliamentary system the prime minister is elected by the legislature, often under the strong influence of the party leadership. Thus, a party's candidate for the head of government is usually known before the election, possibly making the election as much about the person as the party behind him or her.
Another major criticism of the parliamentary system lies precisely in its purported advantage: that there is no truly independent body to oppose and veto legislation passed by the parliament, and therefore no substantial check on legislative power. Conversely, because of the lack of inherent separation of powers, some believe that a parliamentary system can place too much power in the executive entity, leading to the feeling that the legislature or judiciary have little scope to administer checks or balances on the executive.
Although it is possible to have a powerful prime minister, as Britain has, or even a dominant party system, as Japan has, parliamentary systems are also sometimes unstable. Critics point to Israel, Italy, India, the French Fourth Republic, and Weimar Germany as examples of parliamentary systems where unstable coalitions, demanding minority parties, votes of no confidence, and threats of such votes, make or have made effective governance impossible. Defenders of parliamentarianism say that parliamentary instability is the result of proportional representation, political culture, and highly polarised electorates.
Although Walter Bagehot praised parliamentarianism for allowing an election to take place at any time, the lack of a definite election calendar can be abused. In some systems, such as the British, a ruling party can schedule elections when it feels that it is likely to do well, and so avoid elections at times of unpopularity. Thus, by wise timing of elections, in a parliamentary system a party can extend its rule for longer than is feasible in a functioning presidential system. In other systems, such as the Dutch, the ruling party or coalition has some flexibility in determining the election date.
Alexander Hamilton argued for elections at set intervals as a means of insolating the government from the transient passions of the people, and thereby giving reason the advantage over passion in the accountability of the government to the people.

Criticisms of parliamentarianism
Parties in parliamentary systems have had much tighter ideological cohesiveness than parties in presidential systems. It would be difficult for a parliamentary system to have a party like the United States Democratic Party, which until the 1980s was a coalition of Southern conservative Protestants ('Dixiecrats') and urban liberals with no single unified ideology. In a parliamentary system, a party such as this would typically splinter because, if in government, it may be unable to govern effectively. Having splintered, though, the resulting parties might join in a governing coalition.
This form of government is often compared to a Presidential system.

Unicameral system
This table shows countries with parliament consisting of two houses.