This paper reports user requirements for frequency standards for optical communications and reviews physical possibilities for measurement standards to support those needs. A survey of the industrial and regulatory requirements for frequency standards for optical communications was made between October 1991 and January 1992. This was centered on the UK and Europe, but also took in responses from the USA and Japan. Over 70 representatives from 49 organizations were contacted, and a response exceeding 50% was achieved. The main requirement found was a need for two frequency standards per band in each of the 1.5 micrometers and 1.3 micrometers bands, with those in the 1.5 micrometers band needed first, and in the next 3 - 5 years. An accuracy of order 1 part in 109 was desired for laboratory use, with an order of magnitude less for a transfer standard, and an order less again in the field. The physical possibilities for frequency standards in these bands are reviewed, addressing the use of atomic and molecular resonances.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.