During the last decade various asynchronous circuit structures and design methods have been proposed that seem to be quite different. In essence, however, all these methods contribute to solving the same fundamental design problem in one way or another. In this paper we use a simple communication model to figure out what this fundamental design problem actually is and to highlight its roots. We show how each of the related sub-problems can be conceptually solved in the time domain and in the information domain. Having this model in mind we finally develop a common framework to classify the most popular asynchronous design methods and figure out which sub-problem they actually solve and in which respect they differ from each other.