The way people work
I saw this bit in an article recently:
Agile is all about People over Process and you need tools which fit the way people want to work.I'd like to think this is a good general principle for Engineering, not just Agile. That being said, I think there's a balance to be struck between policy/process, and chaos. The goal is to find a good functional model that fits the way people work, then canonize a process, and evolve it over time as situations change. In that context, Agility comes from a willingness to change.