We introduce Hybrid Sequence Charts (HySCs) as a visual description technique for communication in hybrid system models. To that end, we adapt a subset of the well-known MSC syntax to the application domain of hybrid systems. The semantics of HySCs is different from standard MSC semantics. Most notably, we use a shared variables communication model and assume the existence of a continuous, global clock. Similar to their classic counterpart HySCs can be advantageously used in the early phases of the software development process. In particular, in the requirements capture phase, they improve the dialog between customers and application experts. They complement existing formalisms like hybrid automata by focusing on the interaction between the system's components. We outline the key concepts and the usage of HySCs along an example, the specification of an electronic height control system. Then we define the formal semantics of their basic elements.