R.W. Crompton is internationally known for his experimental studies of electron collisional processes in gases and in particular for his measurements of diffusion and drift the precision of which is the result of a systematic attack, extending over many years, on sources of experimental error. The collision cross sections that he and his colleagues have derived from these measurements are now regarded as standard results against which a number of quantum mechanical calculations have been tested. His work is significant not only because the cross sections are precise and absolute but also because they relate to a range of very small energies inaccessible to other techniques.