As software becomes ever more embedded into the fabric of society, more systems are becoming critical to large numbers of people, either by design or unintentionally. Even those that may not be considered safety-critical can have a large impact when they fail (e.g. banking systems). Consequently, software can be critical for a number of reasons, including: safety; security; and mission impact of failure. We would expect criticality, along with software requirements, to emerge from coherent, integrated systems-level analyses that include data, security, mission and safety aspects. We have combined software requirements from a number of sources, including those based on the "4+1" software safety principles and those emerging from security considerations, to produce a single list of top-level expectations that any critical software development would be expected to satisfy. This list provides a simple, unified structure that may, for example, be used to organize audits or promote discussion between customer and supplier.