THE recent development of various methods of modulation such as PCM and PPM which exchange bandwidth for signal -to -noise ratio has intensified the interest in ageneral theory of communication. A basis for such a theory is contained in the important papers of Nyquist and Hartley on this subject. In the present paper we will extend the theory to include an umber of new factors, inparticular the effect of noiseinthechannel, and the saving spossible due to the statistical structure of the original message and due to thenature of the jinal destination of the information _ Reprinted with corrections from The Bell System Technical Journal,Vol.27, pp.379–423 ,623–656 ,July, October, 1948..