The 10 nominated commissioners from the accession states will face the tension of representing national issues at European level, writes Denis Staunton, in Brussels.
The European Commission President, Mr Romano Prodi, has asked the EU's 10 new member-states to submit their nominees for membership of the Commission by the end of next month.
The new commissioners will only serve in the present Commission for six months, starting on May 1st, but are likely to retain their posts when the next Commission takes office in November.
The commissioners will not receive portfolios before November but will each work with two of the present commissioners for three-month stints.
The new commissioners will, however, have full voting rights at Commission meetings, where decisions are taken by a simple majority.
At present, 20 commissioners run 24 directorate generals. However, the next Commission will operate under the terms of the Nice Treaty, which gives each member-state just one commissioner.
Commissioners take an oath of office that pledges them to serve the EU as a whole and forbids them from taking instructions from national governments. The reality is, however, that commissioners are conscious of their home country's national interests and often articulate them at Commission meetings.
Nominated by national governments, commissioners are usually drawn from parties in power and represent an important, informal link between Brussels and the national capitals. The 10 new member-states are alert to the need for ensuring that their first commissioners in Brussels should be first-rate, not least to give their national nominee a good chance to win an important portfolio.
Governments can nominate anyone they choose, but the nominee must be approved by Mr Prodi and by the European Parliament. Mr Prodi has called for at least three of the 10 new commissioners to be women, but only Poland and Lithuania appear likely to propose a woman.
Poland, by far the biggest of the new member-states, is expected to nominate its European affairs minister, Ms Danuta Hubner, who represented Poland at the Convention on the Future of Europe.
One of the key negotiators on Polish membership of the EU, Ms Hubner is popular in Brussels, and is likely to secure an important post in the next Commission.
Although Ms Hubner is widely credited with helping to persuade Poles to vote for EU membership, her critics in Poland complain that she has been too eager to compromise on Polish interests in return for approval in Brussels.
Slovenia is also expected to send its European affairs minister, Mr Janez Potocnik, to Brussels, while Cyprus is likely to nominate its 65-year-old foreign minister, Mr George Iacovou. Estonia's former prime minister, Mr Siim Kallas, is the front-runner for Tallinn's nomination, despite a recent crisis within the coalition in which his party is the junior partner.
Hungary is expected to choose either its former chief EU negotiator, Mr Endre Juhász or the government's representative at the Convention on the Future of Europe, Mr Péter Balázs.
In the Czech Republic, the nominee is likely to be either the foreign minister, Mr Cyril Svoboda or Prague's ambassador to the EU, Mr Pavel Telicka.
Most Slovak commentators favour the country's chief EU negotiator, Mr Jan Figel, but the government has hinted that it may choose a former manager at Coca Cola in Slovakia, Mr Ivan Stefanec.
As the Slovak government's representative at the Convention on the Future of Europe, Mr Figel has developed a profile in Brussels.
The most colourful of the new commissioners could be Latvia's foreign minister, Ms Sandra Kalniete, a former art historian who speaks Latvian, Russian, English and French.
Her books include a work on Latvian textiles and the intriguingly titled Es lauzu, tu lauzi, mes lauzam. Vini luza (I broke, you broke, we broke. They fell apart).