This review summarizes work carried out in the field of color difference measurement, mainly during the period 1960-1980. Starting with the CIE system and the early work of Wright and MacAdam on color discrimination, the review covers the development of perceptually more uniform color spaces such as those of Adams, Saunderson and Milner, Glasser, Hunter, MacAdam, 1964 CIE. The evaluation of these and other color difference formulae during the 1970's, which led to the adoption of the ANLAB color difference equation in 1970 and the CIELAB equation in 1976, is dealt with in detail. The investigations during the period 1970-80 by various workers such as McLaren, Kuehni, Friele, McDonald, etc. To quantify the non-uniformity in color space and produce more useful color difference formulae by optimizations to fit practical color matching data are reviewed. A source list of color difference formulae is appended.