This chapter gives an introduction to the CORAS approach for model-based security risk analysis. It presents a guided walkthrough of the CORAS risk analysis process based on examples from risk analysis of security, trust and legal issues in a collaborative engineering virtual organisation. CORAS makes use of structured brainstorming to identify risks and treatments. To get a good picture of the risks, it is important to involve people with different insight into the target being analysed, such as end users, developers, and managers. One challenge in this setting is to bridge the communication gap between the participants, who typically have widely different backgrounds and expertise. The use of graphical models supports communication and understanding between these participants. The CORAS graphical language for threat modelling has been developed especially with this goal in mind.