Abstract This paper is sort of a confession. Issues of synchrony, asynchrony, and synchronization, arise frequently in designing embedded systems from components, like everyone I knew this for quite a long time. But it is only recently that it went aware of the diversity of such issues, depending on the context. The aim of this paper is to show and explain this diversity by looking at three areas where systems design is of interest, namely : 1/ building software or hardware architectures composed of components interacting asynchronously, 2/ synchronous hardware design from IP’s, and 3/ designing distributed real-time control systems. A large part of this paper relies on other people’s work, I indicate appropriate references in each case. 1 Think synchronously, act asynchronously This is a widely used engineering practice in several important areas where embedded systems are designed. Real-time control systems such as encountered in automobiles or even more in aeronautics, interact ...