This paper is about the role of layered models in IT standardization activities. The layered model is a modeling technique that is widely used although its specific characteristics have received little attention in the literature. The best know example of a layered model is probably the OSI Reference Model for data communications, which also illustrates its prominent role in standardization. The layered model is a highly powerful modeling technique, applicable in large scale system design and development and especially in standardization efforts. We propose the heuristic that successful standards always fit in a clear layered model and we give a number of rules for developing this kind of models.