The concept of the assessment of image quality by means of the optical transfer function (OTF) is traced from the early use of sine wave test charts through to the development of the high precision electro-optical instuments required to test modern optical systems. During the 1950's simple photoelectric equipment based on the conventional nodal slide bench, designed for visual assessment, was widely constructed. During the next decade however very poor agreement was found to exist between OTF measurements made on the same lens by different laboratories largely due to mechanical deficiencies but also because the critical dependence of image quality on spectral balance and on choice of image plane were at that time inadequately understood. The situation is even now complicated by a lack of agreement between designers on how to compute the OTF from the lens data. In spite of these difficulties an acceptable level of agreement is now being reached between laboratories for measurements near the axis and OTF has already proved its value to manufacturers and users of optical systems. It is expected that by increasing the level of international collaboration in this subject it will in this decade be possible to resolve rapidly the few remaining areas of disagreement and to work towards agreeing acceptable procedures for specifying image quality in terms of objective parameters such as OTF.