The Speaker presides over the House of Commons and is responsible for keeping order during debates and ensuring that the rules of the House are obeyed.
The Speaker must always act impartially and protect the right of all MPs to speak during debates.
He or she does not take part in debates and only votes if there is a tie and a casting vote is needed.
The Speaker has three deputies who act in his or her absence.
Elected at the start of each new Parliament by all the members of the Commons, the Speaker will be a respected senior MP.
Once elected, however, the Speaker ceases to represent any political party.
Traditionally, in the event of a general election, the Speaker's seat is not contested by any of the main political parties.
However, the SNP did challenge the current Speaker, Michael Martin, in the 2005 general election, picking up nearly 18% of the vote.
The Speaker lives in the Speaker's House in the Palace of Westminster and presides over Commons debates dressed in a ceremonial black robe.
The Speaker also represents, or speaks for, the House of Commons in its dealings with the monarch and has the responsibility of maintaining the dignity and privileges of the Commons.
The Speakership dates back under its present title to 1377, when Sir Thomas Hungerford was appointed.
Equivalent presiding officers before this time were called parlour or prolocutor, and existed as far back as 1258, when Peter de Montfort is said to have presided over the "Mad Parliament" held at Oxford.
While it can be a difficult role to fulfil today, in years gone by it was downright dangerous - five Speakers were beheaded by order of the King in the Middle Ages and Tudor period.