Locked exterior and interior doors may be encountered by first responders at the site of an active shooter either because of security lockdowns at a school or business or because the active shooter has secured the doors from the inside. First responders must have received the knowledge and equipment needed to breach various types of doors, locks, or barricades. Officers must know how to determine whether a door opens in or out and what type of tool is appropriate for forcing open each type of door. This article provides instruction in how to determine whether a door swings in or out and describes the features and uses of common breaching tools. One such tool is the Halligan tool, which can be used in a variety of ways; however, the primary function of the Halligan tool is to open outward-swinging doors through prying. This article describes this technique in detail. Another tool, the sledgehammer, can be used with the Halligan tool and by itself to break glass and breach an inward-opening door. The various uses and techniques for using the sledgehammer are described. A third tool, the battering ram, is the most common manual breaching tool used for inward-opening doors. Techniques for using the battering ram are also described. In addition to responding to a call regarding an active shooter, patrol officers may encounter a hostage situation or barricaded gunman. The article discusses the use of breaching techniques in such a situation.