In politics, a party leader is the most powerful official within a political party. The leader speaks to their designated political party, while acting as the party representatives. The party leader is typically responsible for managing the party's relationship with the general public. As such, he or she will take a leading role in developing and communicating party policy, especially election platforms, to the electorate. He or she is also typically the public face of the party and the principal media contact.
In many representative democracies, party leaders compete directly for high political office. It is thus typical in such states (e.g., in the Westminster system) for the party leader to seek election to the legislature, and, if elected, to simultaneously serve as the party's parliamentary leader.
In Canada, all major parties elect their leaders at certain age.
The leaders of Communist Parties often hold the title of General secretary (e.g. General Secretary of the Communist Party of the Soviet Union and General Secretary of the Communist Party of China) and the officeholder is usually considered the paramount leader of China. On 15 November 2012, Xi Jinping was appointed General Secretary of the Communist Party of China at the 18th Communist Party national congress. 
In the Netherlands, the party leaders are the most senior politicians within the political parties in the Netherlands. The leaders outwardly act as the 'figurehead' and the main representative of the party. Within the party, they must ensure political consensus. At election time the leader is always the Lijsttrekker (top candidate) of the party list. Outside election time the leader can serves as the Opposition leader. Geert Wilders, the Leader of Party for Freedom, is the Leader of the Opposition. In the People's Party for Freedom and Democracy (VVD) and the Labour Party (PvdA) the leader is often the Parliamentary leader in the House of Representatives. Leaders became a Minister in a Cabinet.
The method of selection of the party leader varies from party to party, though often it will involve an election involving all or part of the party membership. In some parties, only current members of the parliamentary party, or particular party office-holders, may vote; in others, such as the British Labour Party, though the entire membership is eligible to vote, some electors may have a much larger share of the vote than others (see also Superdelegate for a similar concept). If only one candidate emerges, he or she is said to have been "elected by acclamation" or "ratified" by the general membership (sometimes the term "anointed" occurs informally or in media discourse).
The Prime Minister of the United Kingdom, Theresa May, gained the position on 13 July 2016; she had served as the party leader of the Conservative Party since 13 July 2016. Jeremy Corbyn is the party leader the Labour Party, serves as the Leader of the Opposition.
In the Gilded Age (late 19th century in the United States), the government was known as Bossism. This government entailed powerful political machines, run by so-called "bosses" who awarded political positions to their associates (one example being Tammany Hall which was run by Boss Tweed) This kind of political system is also referred to as a particracy. Party leaders in the United States mostly refer to the President, Vice President and leaders of the Congress in both parties.
President Donald Trump, Vice President Mike Pence, Speaker of the United States House of Representatives Paul Ryan, President Pro Tempore of the United States Senate Orrin Hatch, House Majority Leader Kevin McCarthy, House Majority Whip Steve Scalise, Senate Majority Leader Mitch McConnell and Senate Majority Whip John Cornyn are the party leaders of the Republican Party. The Democratic Party is chaired by Tom Perez. Chuck Schumer is the current Senate minority leader.Nancy Pelosi is the House Democratic Leader. 44th President Barack Obama (until January 20, 2017), of the United States, 47th Vice President Joe Biden (until January 20, 2017), Senate Minority Leader Harry Reid (until January 3, 2017), Senate Minority Whip Dick Durbin, House Minority Leader Nancy Pelosi and House Minority Whip Steny Hoyer are the party leaders of the Democratic Party.