If we are to manufacture products with molecular precision, we must develop molecular manufacturing methods. There are basically two ways to assemble molecular parts: self-assembly and positional assembly. Self-assembly is now a large field with an extensive body of research. Positional assembly at the molecular scale is a much newer field which has less demonstrated capability, but which also has the potential to make a much wider range of products. There are many arrangements of atoms which seem either difficult or impossible to make using the methods of self-assembly alone. By contrast, positional assembly at the molecular scale should make possible the synthesis of a much wider range of molecular structures.

One of the fundamental requirements for positional assembly of molecular machines is the availability of molecular parts. One class of molecular parts might be characterized as molecular building blocks (MBBs). With an atom count ranging anywhere from ten to ten thousand (and even more), such MBBs would be synthesized and positioned using existing (or soon to be developed) methods. Thus, in contrast to investigations of the longer term possibilities of molecular manufacturing (which often rely on mechanisms and systems that are likely to take many years or even decades to develop), investigations of MBBs focus on nearer term developmental pathways.