Computers are key elements of many systems, including utilities and transportation. Such systems are reliant on software to ensure safety, i.e. to protect human life and health. It is important for designers both to achieve safety and to demonstrate that they have done so. This chapter addresses both issues, including ways of demonstrating safety using safety cases. Software also has a role in system availability, reliability, and cyber security. We use the term dependability for this broader set of system attributes; the chapter also considers how to address these attributes, and trade-offs between them, using dependability cases Finally, the chapter considers some of the emerging challenges of achieving and demonstrating the safety of systems of systems, and of autonomous systems.