Nanotechnology comprises technological developments on the nanometer scale, usually 1 to 100 nm (1/1,000 µm, or 1/1,000,000 mm). A possible way to interpret this size is to take the width of a human hair, and imagine something ten thousand times smaller. The term has sometimes been applied to microscopic technology.
Nanotechnology is any technology which exploits phenomena and structures that can only occur at the nanometer scale, which is the scale of several atoms and small molecules. The United States's National Nanotechnology Initiative website defines nanotechnology as "the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications."