After World War II, communication and control engineering reached a high level of development. The next step may be the recasting and unifying of the theories of control and communication in the machine and in the animal on a statistical basis. This monograph represents one phase of the new theory pertaining to the methods and techniques in the design of communications; it was first published during the war as a classified report to the National Defense Research Committee. It is an attempt to unite the theory and practice of two fields of work that are of vital importance and have a complete natural methodological unity, although they draw their inspiration from two entirely distinct traditions and are widely different in their vocabulary and the training of their personnel-time series in statistics and communication engineering.