The transmission of pictures by pulse code modulation (PCM) has been investigated by various researchers1, 2 for more than a decade. Recently, interest has reached a new high, partly because of the possible military and space applications. The purpose of the present article is to describe briefly some of the research work being carried on in Pcm picture transmission at the Cognitive Information Processing Group (CIPG) of the Research Laboratory of Electronics, Massachusetts Institute of Technology. Many other groups, notably the Bell Telephone Laboratories researchers, are also working extensively in this area.