Typically we think about securing things -- a system, a network, our homes, sometimes even our personal content like email or files on a laptop. That's security as a place, a well-drawn boundary around what is secured and what lies at risk. Security, however, is itself a thing, something that evolves as risks, components and the relationships of those components change, and as new risks are discovered and tolerances for those risks tested and cost-adjusted. Glenn's systemic security patterns reflect outstanding systems engineering -- thinking about security in a dynamic context, not a set-it-forget-it mentality.