This chapter considered the most important issues in systems and network security. Security principles and basics were explained, and security was identified as a process, not a product. Practice shows that the weakest link in the security chain are the humans, not the computers. Contrary to popular opinion, computers do what they are told most of the time; humans don’t. And in your fight for computer security, the humans are your friends and your enemies. Work with your friends against your enemies, because computers don’t have brains. The people behind them do.