How can nanotechnology promise to build products with both extreme precision in structure, and environmental cleanliness in the production process?

Traditional manufacturing builds in a "top down" fashion, taking a chunk of material and removing chunks of it - for example, by grinding, or by dissolving with acids - until the final product part is achieved. The goal of nanotechnology is to instead build in a "bottom-up" fashion, starting with individual molecules and bringing them together to form product parts in which every atom is in a precise, designed location. In comparison with the top-down approach, this method could potentially have much less material left over, greatly reducing pollution.

In practice, both top-down and bottom-up methods are useful and being actively pursued at the nanoscale. However, the ultimate goal of building products with atomic precision will require a bottom-up approach.