Differential pulse-code modulation (DPCM) is a technique for bit-rate reduction. This report discusses the principles of DPCM and its application to television. An investigation of the use of DPCM with sub-Nyquist sampled composite PAL video signals is then described. The usefulness of computer optimization techniques is established and practical development work described. It is concluded that three-dimensional predictors, of a complexity not previously envisaged to be worthwhile, offer significant improvements. Two systems meeting practical requirements for 34 and 68 Mbit/s transmission 'packages' were developed and subjectively assessed.