The miniaturization revolution in silicon-based microelectronics will soon approach its nanometer-scale limits, making it increasingly urgent to find alternative materials and less costly methods of manufacture to assist or supplant \"top-down\" lithography. The likely successor technology will involve molecular electronics: conductive molecules and conductive, self-assembled molecular-scale structures. Recent advances in molecular-scale diode switches, transistors, logic circuits, and memory cells as well as techniques for \"bottom-up\" assembly in very large numbers point the way towards ultra-dense molecular-scale electronic computers in the foreseeable future. As well, progress in nanoscale sensors may allow the development of \"smart matter\" with molecular electronics as its enabling technology. This volume explores these possibilities in its discussion of experiment, theory, design, fabrication, operating principles, and applications of molecular-scale electronics.