Nanotechnology is technology on the scale of the nanometer. Physically, this relates to sizes of only a few atoms' width. Implementing nanotechnology in its fullest sense would require the ability to directly manipulate atoms or molecules. It is sometimes called Molecular nanotechnology to distinguish it from MEMS.
Ralph Merkle has compared today's chemistry to an attempt to build interesting Lego brick constructions while wearing boxing gloves. Because we currently have no tools that allow us to place a particular atom in a particular place (so that it bonds in a predictable way with another particular atom), we must work with statistically large numbers of atoms. As a result, when we cause a particular chemical reaction, we frequently get a mix of several different product species. The reaction is often followed by a physical filtering process to extract the species we actually wanted, with the other species discarded as waste. Nanotechnology could therefore offer much cleaner manufacturing processes than are available with today's bulk technology.
The first mention of nanotechnology (not yet using that name) was in a talk given by Richard Feynman in 1959, entitled There's Plenty of Room at the Bottom. Feynman suggested a means to develop the ability to manipulate atoms and molecules directly, by developing a set of one-tenth-scale machine tools analogous to those found in any machine shop. These small tools would be used to develop and operate a next generation of one-hundredth-scale machine tools, and so forth. As the sizes get smaller, it would be necessary to redesign some tools because the relative strength of various forces would change. Gravity would become less important, surface tension would become more important, van der Waals attraction would become important, etc. Feynman mentioned these scaling issues during his talk. The feasibility of his proposal has never been effectively refuted.
The term nanotechnology was first used by K. Eric Drexler in his book Engines of Creation: The Coming Era of Nanotechnology (text available online ) ISBN 0-385-19973-2. In the fourth chapter, Drexler introduces self-replication (see also Von Neumann machine), another powerful premise of nanotechnology. Cells build copies of themselves in order to reproduce, and human-designed molecular robots could do the same thing. This would mean that after the enormous research expense of designing and constructing the first molecular robot capable of self-replication, the next trillion robots would cost no more than an equal mass in vegetables.
These same generally capable robots, called assemblers, could then build more special-purpose objects that humans would find directly useful: houses, kitchen widgets, cars, furniture, medical instruments, spaceships, etc. Like the assemblers themselves, these products would be extremely cheap by comparison with those produced today. Specifically, the inputs to any such manufacturing process would be raw materials (atoms), energy, design software, and time.
Whilst progress has been made in producing ever-smaller computer circuits and manipulating individual atoms, constructing real nanomachines is currently well beyond our present capabilities and are generally believed to be at least decades away. Many doubt that controllable self-replicating nanobots are possible at all, citing the possibility of mutations removing any control and favouring reproduction of the mutant pathogenic variations. Advocates counter that bacteria are designed to mutate, and nanobot mutation can be prevented by common error-correcting techniques used in computers today.
Despite its current infeasability, there has been much speculation about the impact of nanotechnology on economics and law. Some believe that money would cease to be of use and taxation would cease to be feasible. Others conjecture that nanotechnology would elicit a strong public-opinion backlash, as has occurred recently around genetically modified plants and the prospect of human cloning. Whatever the exact effects, nanotechnology is likely to upset existing economic structures, as it makes some currently scarce items and services into commodities.
Of course, nanotechnology is not without its risks. In addition to enabling the development of much cheaper and more destructive conventional weapons, nanotechnology also offers the possibility of weapons that operate by self-replication, as viruses and cancer cells do when attacking the human body. There is general agreement that self-replication should be permitted only very controlled conditions.
In light of these dangers, the Foresight Institute (founded by Drexler to prepare for the arrival of future technologies) has drafted a set of guidelines  for the ethical development of nanotechnology.
Drexler and others have extended the ideas of nanotechnology with two more books, Unbounding the Future: the Nanotechnology Revolution  and Nanosystems: molecular machinery, manufacturing, and computation . Unbounding the Future is an easy-to-read book that introduces the ideas of nanotechnology in a not-too-technical way, and Nanosystems is an in-depth analysis of several possible nanotechnological devices, with thorough scientific analyses of their feasibility and performance. Another notable work in the same vein is Nanomedicine by Robert Freitas. Nanotechnology has also become a prominent theme in science fiction , for example with the Borg in Star Trek, and Neal Stephenson's book The Diamond Age.