Unless proper control is exercised in limiting the amplitude of jitter in future digital networks, serious degradations can arise. The important sources of jitter are identified and described. Trie manner in which jitter accumulates in a digital network is discussed with particular emphasis being given to accumulation along transmission systems. A brief review is given of the current status of jitter studies within international organizations (CCITT and CEPT).† The jitter control and specification philosophy for digital networks and equipments based on the 2048-kbit/s hierarchy is outlined.