This book is over twenty years old now, and is regarded, quite rightly, as a classic. K. Eric Drexler takes us on a dizzying tour of nanotechnology, its potential and applications. His claim is simply this: that nanotech will completely transform our world in ways we can hardly dream of....and that those changes are imminent.

However, don't expect a dry, technical book. Drexler touches on many related subject areas: the evolution of ideas, the spreading of memes, biology, longevity, ethics and much more. There are fascinating chapters on each, and the one which is most relevant, looking back to 1987, is the chapter about how seemingly-insuperable technological challenges are always overcome in the end, and how solutions are arrived at. We have already seen technological advances which would have seemed impossible twenty years ago when this book was written - and twenty years is a very short timescale indeed.

There are chapters about how society will deal with the new age, and what problems nanotechnology could cause if the implications of it are not managed by society in an intelligent manner - and that might be the first big problem. Drexler envisages a future world where nanomachines manufacture other nanomachines, where buildings are "grown" in just weeks from nanocultures, where constantly-vigilant nanomachines, roaming our bodies, identify tumours and eliminate them at the cellular level. When he turns his attention to space travel, we have asteroids automatically mined by nanomachines, interstellar spacecraft built from nanomaterials and the perfect spacesuit.

The coming era of nanotechnology, says Drexler, will give humanity an age of plenty, a golden age unlike any seen before in history. It's a wonderfully imaginative, inspiring vision, but will it ever become reality, and if so when? Wisely, Drexler does not commit himself to answering that question. He merely says that scientists already *know* what properties the nanomachines of the future will have to have; the rest is "just engineering".

The first step towards this golden age will be the creation of molecule-sized Assemblers and Replicators. The former will be able to build objects from the atomic level upwards, positioning individual atoms precisely to build materials of perfect purity. The latter will be able to build other nanomachines from scratch. Both types of nanomachine will emerge from new and powerful nanotechnologies: Drexler seems to think that their appearance is inevitable. Once they exist, everything else will follow. Nanomachines will be able to manufacture any object you would like from scratch, building them from pure and flawless materials; they will repair the environmental damage we have wreaked upon our planet; they will allow people to live forever.Such is the scope of Drexler's vision.

The book also contains some extremely interesting chapters which place nanotech in a social context, and how we might control - or contain - any possible threat from nanotech weapons, although some of these discussions take place in the context of American and Soviet politics, which obviously dates the book somewhat. Drexler also gives us a vision of future technology with regard to computers, and some of his descriptions are similarly dated: the predictions about hypertext - a new concept in 1987 of course - and the proliferation of information have already been far surpassed in the internet age.

So, twenty years on in 2008, how far have we gone down the road to nanotech? The only visible commercial nanoproducts are used in the manufacture of items such as face creams, laser printer toner, baseball bats and other consumer goods. It's not - yet - the inauguration of the "golden age". However, scientists *are* creating miniature machines which get ever-smaller and more capable. To arrive at Assemblers and Replicators will require miniaturisation and computing techniques we can only dream of today, but perhaps Drexler is right: there are no fundamental *physical* barriers to true nanotech. It's all just a matter of time, and, after all, living creatures have been using natural replicators and assemblers since DNA and RNA first evolved. All we need to do is to learn how to build our machines on similar scales.

However, wonderful as this book is, ultimately one is left with the feeling that nanotechnology as described by Drexler, like fusion power, is always just around the corner. Having said that, reading this excellently-written book one cannot fail to be infected with Drexler's enthusiasm for the possibilities. Will his vision of a glorious future, an unprecedented golden age for humankind, come to pass? It would be wonderful to think so. But......

If you are looking for a book about the future of technology, and not just nanotech, this book is an essential read.