Developments in European science and science policy suggest that a new landscape is forming, one over which scientists can move as freely as they already do between Massachusetts and California.

The great scientific traditions of Europe have always had strong national identities. One thinks of Pasteur as French, Newton as British, Planck as German. But in moving towards an economically unified Europe, some national sovereignty had to be given up to serve a more communitarian vision. That same evolution is now taking place in science, as a powerful movement towards unified European research takes shape.

In a recent editorial in Le Monde, several Nobel Prize winners - including Francois Jacob, the French biologist, Bengt Samuelsson, the Swedish biochemist, Aaron Klug, the British biochemist, and Rita Levi Montalcini, the Italian developmental biologist - called for a restructuring of science policy that would double support for science, renew the focus on basic research and fund centres of excellence that would be regional and not national. Soon afterwards, the European Commission pointed out that European countries together produced proportionally more scientists then the US - but that scientists constituted a much smaller proportion of the working population. To help retain scientists, the Commission has advocated increased European Union investment in research and urged European co-operation to stop the "brain drain".

This growth of scientific collaboration in Europe is encouraged by the EU's sixth research framework programme, which provides grants to support work throughout the Union. The trend towards breaking down national borders should also be evident at a new pan-European event - EuroScience 2004 - taking place in Stockholm a year from now.

All this is good news but more work is needed in three areas. The priorities of a future European research entity should be restructured; governments both sides of the Atlantic should co-operate to plug any "brain drain" of talent away from Europe; and science policy needs to follow science along its cross-border course.

Some European scientists are reported to be dissatisfied with the balance of basic and applied research in the EU's framework programmes. They want more of the former and less of the latter. This dissatisfaction is fuelling discussion on the formation of a European research council, which might play a pan-European funding role like that of the National Science Foundation in the US. But if such a council is to develop, there needs to be a careful examination of the weight of different scientific fields in its research portfolio.

The US government should welcome these developments but it must also change its own position to assist the European science union. That means helping to tackle the problem of "brain drain", which received much attention in the 1960s but slipped out of view as European research expenditure increased and laboratories grew stronger. Many European commentators claim it has reappeared.

To slow it, US institutions need to ignore, at least for a time, the temptation to conduct overseas raids on scientists to fill permanent positions. An increased international scientific exchange will support, rather than inhibit, the equitable distribution of talent; and US science and immigration policies should be drawn in ways that ease movement of graduate and post-doctoral scientists in both directions. At the moment, the increasingly delicate visa situation - exacerbated by new interview requirements imposed by the US authorities - and the well publicised political differences between the US and Europe are impairing scientific exchange.

Last, the knowledge needed to construct a European science policy based on regions rather than nations must come from scientists themselves. Regional centres of excellence might provide a structure for policy discussion. But scientists still face the dilemma that while science is increasingly carried out across borders, science policy is still made by nations. The people best placed to construct a European science policy that brings together broad issues (such as the desirable balance between basic and applied projects) and narrower ones (such as stem cell research) are its leading scientists. It is a task worthy of their best efforts. The writer is editor-in-chief of Science, the international journal of the American Association for the Advancement of Science.