Most software development methods define notations for modelling global behaviour. Many of these notations use interaction diagrams to model possible sequences of interactions between a system and its environment, or between the objects of the system. Other methods use structured textual descriptions or regular expressions for specifying use cases or use scenarios. Although many methods use similar notations, there are often substantial differences in their underlying concepts and in the content expressed by the diagrams. On the other hand, completely different notations use sometime the same concepts and show the same aspects of the global behaviour of a system. In this document we investigate the characteristics of different notations. We show what their underlying concepts are and how they relate to each other. Finally, we give an overview of the techniques that are used by some of the current object-oriented analysis methods for modelling global behaviour.