Today's firearms-training simulators offer options such as custom-made scenarios, low-light capabilities, return-fire capabilities, picture-in-picture, heads-up displays, non-tethered recoil weapons, and the traditional shoot/don't shoot scenarios. The wide range of options available make simulators a viable training tool for almost all disciplines and types of law enforcement training. Most successful and comprehensive firearms training programs include common features: a history of active shooting events, small-team movement, contact-team responsibilities, room-clearing techniques, active shooter v. hostage or barricade situations, and rescue team tactics and responsibilities. The more comprehensive courses combine the traditional classroom setting with dynamic, scenario-based exercises. Scenario-based exercises in active shooter training create a sense of realism that is difficult to create in any other training format. With the development of technologies such as Simunition FX Marking Cartridges, scenario-based exercises have become much more realistic and easier than ever to conduct; however, there are several limitations and considerations that must be addressed in order that such exercises be effective. First, safety of the participants must have top priority. Second, there must be instructors, safety officers, role players, and students present during the training session to ensure safety. Third, force-on-force training can be equipment-intensive. Safety equipment must be used for all participants, and props are required for many scenarios. Finally, a suitable location for holding force-on-force training is also required; a school or office complex is most desirable. This article includes descriptions of the various types of firearms simulators currently available on the market.