The overall approach in this document is biased towards concept design and development phases, since the significant and fast-evolving changes ongoing today in ATM represent the major driver for system safety assessment. Nevertheless, most of the techniques can be (and often are) just as easily applied to existing systems. A good number of the techniques themselves deal with Human Factors and human error aspects of safety, as the human element is a critical determinant of safety in current and future ATM, and cannot be ignored in safety assurance activities.