European Union leaders have agreed to appoint Polish Prime Minister Donald Tusk to head the European Council and Italian Foreign Minister Federica Mogherini to lead the bloc's high-profile foreign affairs arm.

With former Luxembourg premier Jean-Claude Juncker already named as the new chief of the European Commission, the EU's executive arm, the 28-member bloc now has its top team in place.

Here is a summary of the three key positions:

Chair of the European Council

The Council is the political arm of the EU, bringing together member state leaders and their top officials to make the bloc's overall policy decisions, which are then implemented by the European Commission.

The Council chair, a post also created in 2009 by the Lisbon Treaty, is currently held by Belgium's Christian Democrat Herman Van Rompuy, a former premier who has proven to be an adept negotiator and conciliator, essential qualities when searching for an often elusive consensus among the 28 political leaders.

The Council has taken on a greater role since the 2008 global financial crisis brought the economy to its knees and nearly brought down the euro.

The Council head serves initially for two-and-a-half years, a term which can be extended once.

EU Foreign Policy Chief

The European External Action Service was also created by the 2009 Lisbon Treaty, to give focus to the much-enlarged EU's international role and interests.

It coordinates the EU's foreign and defence policy priorities, a difficult mission given that many member states, especially the biggest ones such as Britain and France, are notoriously protective of their own place in the world.

Formally known as the EU's "High Representative", Britain's Catherine Ashton has played a major role in many of the top international issues, from the Middle East to Iran nuclear talks and the crisis in Ukraine.

The High Representative serves a five-year term and counts also as a member of the 28-seat European Commission.

President of the European Commission

The European Commission is the executive arm of the EU, acting as its civil service to draw up the legislative proposals needed to put European Council decisions into effect. It also initiates policy proposals.

As such, it has huge influence, although this has been eroded to some extent in recent years with the setting up of the European Council and by Parliament's new-found oversight powers since 2009.

The Commission, housed in the huge Berlaymont building in the Schuman district of central Brussels, is very much the public face of the EU and the one which comes in for most public criticism.