For many years, scientists have imagined schemes for creating molecular electronic devices. In most instances, the intended capability of the molecular structure has been to switch an electron current on and off. Molecular building blocks, if linked together to form logic functions (AND, OR, NAND, and so on), would seem to lead to a computer of ultimate miniaturization. A simple estimate suggests it might be possible to make molecular-based computers about 1000 times smaller than silicon-based computers. Some key steps have recently been made toward achieving this goal. However, it is not yet known whether the molecular electronics scenario is ultimately reasonable.