When the requirements and the interaction design of a system are separated, they will most likely not fit together, and the resulting system will be less than optimal. Even if all the real needs are covered in the requirements and also implemented, errors may be induced by human-computer interaction through a bad interaction design and its resulting user interface. Such a system may even not be used at all. Alternatively, a great user interface of a system with features that are not required will not be very useful as well.Therefore, the primary motivation of this tutorial is to improve system development in practice both regarding requirements engineering and interaction design, especially facilitating the latter. We argue for combined requirements engineering and interaction design, primarily based on usage scenarios in the sense of sequences of actions aimed at accomplishing some task goal. However, scenario-based approaches vary especially with regard to their use, e.g., employing abstract use cases or integrating scenarios with functions and goals in a systematic design process. So, the key issue to be addressed is how to combine different approaches, e.g., in scenario-based development, so that the result is an overall useful and useable system. In particular, scenarios are very helpful for purposes of usability as well.