Contemporary industrial control systems no longer operate in isolation, but use other networks (e.g., corporate networks and the Internet) to facilitate and improve business processes. The consequence of this development is the increased exposure to cyber threats. This paper surveys the latest methodologies and research for measuring and managing this risk. A dearth of industrial-control-system-specific security metrics has been identified as a barrier to implementing these methodologies. Consequently, an agenda for future research on industrial control system security metrics is outlined. The “functional assurance” concept is also introduced to deal with fail-safe and fail-secure industrial control system operations.