This document discusses approaches to improving security through "red teaming" or adversary simulation. It defines red teaming as taking both an adversarial approach and mindset through tactics like computer simulations and vulnerability probes. The origins of red teaming in military war games from the 1960s are described. Examples of both red team failures, like a failed hostage rescue mission due to lack of planning, and successes, like security tests by the NYPD, are provided. The document outlines challenges to effective red teaming like overcoming groupthink and communicating risk. It stresses the importance of emulating realistic adversary tactics, techniques and procedures to provide useful security evaluations. Overall resources on red teaming techniques and a hypothetical red team exercise are presented.