We interpret "mission assurance" to mean the guarantee that Mission Essential Functionality (MEF) provided by an information system is continued despite partial failures and other accidental or maliciously induced changes in the system or its operating environment. MEF can be threatened when the Quality of Service (QoS) delivered by the information system drops below useful levels, when the security and Information Assurance (IA) of the system is compromised, or both. Key enablers of mission assurance under this interpretation are the ability a) to detect when MEF is in jeopardy and b) to remain within "regions of usefulness" in terms of QoS and IA. We describe an approach to managing mission assurance, and the underlying concepts, methodology and runtime support needed to realize the above mentioned enabling capabilities. Keywords-mission assurance, cyber-security; quality of service; runtime assessment; runtime adaptation