This paper extends the considerations of the author’s paper Safety-Critical Design Techniques for Secure and Reliable Systems to security-critical programs. Though, traditionally, a strong distinction has been drawn between safety and security, in the post-9/11 era many systems with safety requirements must also take security into account. Safety-critical software will need to satisfy security-based standards, and high-security software reused in safety-critical systems will need to satisfy safety-based standards. This paper explores the impact of these dual trends on software development.