No longer the talking shop it once was, the European Parliament is one of two EU institutions that has the power to pass laws.
Laws are proposed by the European Commission, made up of one representative from each member state, but it is the job of the Parliament and the Council of Ministers to say whether or not the law should take effect.
In the majority of cases, the Parliament gets equal weighting to the Council of Ministers, which represents national governments.
However in some sensitive areas like foreign affairs, the Council of Ministers has the primary role, with the Parliament merely given a consultative role.
The Council of Ministers is the other law-making institution
MEPs vote on proposed laws at their monthly plenary (full) sessions, where debates are also held on matters of topical interest.
Before going to plenary, the Parliament's position on a law will have been thrashed out in meetings of one of the Parliament's committees, with the "rapporteur", or report author, writing the report on the proposal.
Less controversial reports are often debated solely at committee stage, with the plenary being used for a rubber stamp vote to approve the committee position.
Votes can be taken on a simple show of hands, however if the President is unable to determine a majority from this, he or she will call for an electronic vote to secure an exact result.
If requested by a political group or at least 40 MEPs, a roll call vote may also be taken, which sees the individual vote cast by each MEP recorded and published in the minutes of proceedings.
As well as passing legislation, the Parliament has increasingly used its so-called powers of "own-initiative" to come up with its own idea for new laws, contained in non-legislative reports.
However, it is still up to the Commission to decide whether or not the proposal is worth taking further.
Checks and balances
The European Parliament has an important role in scrutiny and acting as a check on other branches of the European Union.
MEPs have the power to approve or reject the nominee for President of the Commission, and they must also endorse the College of Commissioners, in other words the rest of the Commissioners as a whole. Each nominee for Commissioner must face a grilling from the relevant parliamentary committee to assess the capabilities and "European-ness" of the nominee. On at least two occasions this has led to two nominees being withdrawn.
The Parliament can also call a vote of no confidence, known as a censure motion, in the Commission, forcing the Commissioners as a whole to resign. The threat of censure led to the Santer Commission resigning en masse in 1999.
Another area where the European Parliament has a key role to play is approving the annual Budget of the EU. The Budget - which works on a January to December basis - must be signed off by the President of the Parliament, before it can be adopted.
Around three quarters of the EU's budget comes from contributions from each member state. For example in 2005, the UK contributed £3.6bn, about £60 per person.
The rest of the budget comes from customs duties on trade with non-EU countries as well as a very small proportion from VAT in each country.
It is also up to the European Parliament to "discharge" the EU's budget every year - in other words to assess the effectiveness of how each EU institution spent its money.
With a budget of around 130bn a year to deal with, looking after the EU's money is a power that MEPs guard jealously.