Guide to the European Parliament
The parliament amends, approves or rejects EU laws, together with the Council of Ministers.
The process of "co-decision", by which a law is only passed when approved by both bodies, applies in areas including consumer protection, the single market, workers' rights, asylum and immigration, agriculture, the environment and animal welfare, but not foreign policy.
The parliament also shares authority over the EU budget with the Council of Ministers and supervises other EU institutions, including the Commission. It vets new commissioners, and can sack the commission en masse.
Under the Lisbon Treaty the parliament's co-decision powers were enhanced, to give it a bigger say over agriculture and the budget.