It has often been suggested that operating logical circuitry at low temperatures would have many advantages. The purpose of this paper is to evaluate such suggestions quantitatively. Changes in physical properties of materials upon cooling to low temperatures have been analyzed to determine their impact on the parameters which control the performance of logical circuitry. The following topics have been considered: electrical conductivity, thermal conductivity, thermal energy, heat transfer, superconductivity, liquid helium, low-gap high-mobility semiconductors, and thermal activation of atomic motion. Copyright © 1970 by The Institute of Electrical and Electronics Engineers, Inc.