Critical infrastructures are complex, interlinked socio-technical systems, with impact often crossing state borders. Their protection involves governments and business organisations, interacting in the application of a broad variety of measures to provide safety and security while investing a considerable amount of public and private resources. This paper examines the challenge of making respective policy and investment decisions transparent, and a sample of methods and tools used to facilitate decision making. It also calls for contributions to a knowledge portal on security and safety of critical infrastructures.