There hasn't been anything quite like it in the history of science. Over the past three years, in Europe, the United States and Australasia, a plethora of groups of scientists and other citizens have discussed nanotechnology in extended exercises in 'public engagement'. These initiatives have arisen partly because of the acute awareness by many that all is not as it should be either in the degree of trust in science and technologies on the part of the public, or in confidence in nanotechnology in particular.

As documented in a report published last week (see http://www.involve.org.uk/negreport), these initiatives have a number of common features. Definitions of the word 'nanotechnology' have been chewed over, optimism expressed that nanotechnology can benefit mankind, but — most importantly — concerns have been expressed about a lack of knowledge and regulation surrounding the impact of nanoparticles on health and the environment.

Equally notable were common outcomes for participants, where members of the public and scientists reported how much they had unexpectedly gained in understanding each others' perspectives. Scientists appreciated how non-scientific participants were constructively interested and able to get to grips with key aspects of a complex subject. The latter, meanwhile, usually starting from zero, gained knowledge about what scientists are doing and about their motivation, and a greater awareness of the potential impacts — both real and hyped.

But what's the point of such engagement? One positive example inspired many subsequent activities: the 2004 report on nanoscience and nanotechnology by the British Royal Society and the Royal Academy of Engineering. This was productive not only in its content but also in the way the various processes of engagement enhanced its public credibility and helped ensure that the questions it addressed were of appropriate scope.

A more recent example was a series of 'Nanodialogues', workshops conducted by the UK think-tank Demos unveiled last week (see http://www.demos.co.uk/publications/nanodialogues). One workshop, involving Unilever, showed how issues of corporate social responsibility arise not only in manufacturing processes and products but also in corporate R&D. Another, conducted in a village near Harare in Zimbabwe, demonstrated how remote from reality are some claims made for nanotechnology's potential impact on water purification in the developing world.

Most encouraging for researchers was the strong support by public participants for fundamental science.

A nanodialogue in Swindon involved engagement between 14 local citizens and scientists funded by two UK research councils based there. Here was an example of true 'upstream engagement', the idea — often suspiciously received by scientists — that both the public and scientists have something to gain from discussing future research prospects as an input to research funding. Most encouraging for researchers was the strong support by public participants for fundamental science.

A taste of true upstream thinking by nanoscientists can be found in blogs at http://ideasfactory.wordpress.com. These feature futuristic nanotechnology concepts, including software-controlled assembly of a variety of building-blocks (small molecules to nanoparticles) linked by covalent bonds, and the development of a flexible machine, computer language and compiler as an assembler of molecules and materials under atomically precise control.

These are potentially powerful enabling technologies. To take a view on their risks or values, either as a scientist or as a citizen, depends on imagined contexts of application. The benefit of the public engaging with scientists years or even decades ahead of the arrival of such technologies lies in the broadening of the bases of knowledge, mutual trust and — most importantly — critical appraisal. One challenge now is how to allow a much larger proportion of the public to share in those benefits.

Few governments have put solid investment in the one type of research most consistently and urgently demanded by these groups — on the health and environmental risks of technologies already embedded in hundreds of products on store shelves. Commendably, a new Australian initiative in nanotechnology research includes such investment.

Regrettably, the governments of two countries that have taken strong leads in nanotechnology — the United States and Britain — have failed to respond. These governments and others not only need to act on this outcome of public engagement but must also integrate such processes into their departments' and agencies' activities.