Of the EU's triumvirate of institutions, the Council of Ministers, the Commission and the European Parliament, the latter wins the most important extension of its powers under the new treaty.
MEPs wield most legislative power when they are operating in the process known as "co-decision", in which they are "co-legislators" with the Council of Ministers in the right to a final say over new laws. If agreement between the two is not possible after conciliation talks, the Parliament may block legislation.
The scope of co-decision has been significantly expanded in the treaty to encompass most of the new powers created by it, but also extending the process to fields where it has traditionally not been used.
Those areas where MEPs gain new co-decision powers include legislation on employment, social policy, freedom of information, countering fraud, freedom of movement, various internal market regulations, transport, implementation of research decisions and development policy.
The treaty cuts the numbers of legislative procedures from over 20 to three, while streamlining co-decision.
MEPs also gain some additional powers over the budgets in the foreign policy and justice co-operation fields
The treaty sets a ceiling of 700 MEPs in the Parliament after enlargement (626 now), and requires the Parliament to draw up proposals for a harmonised system of elections.
