Ballistic weapons cause many deaths and critical injuries worldwide. Knowledge of the physics behind these weapons can help emergency clinicians better understand the magnitude of their patients’ injuries. Understanding the type of projectile fired, the distance from the target, and the number of shots fired will help determine the pattern of injury. While the velocity of the projectile is important, the injury patterns are similar regardless of the speed of the bullet, and higher-velocity weapons do not necessarily impart greater injuries. The permanent cavity causes obvious tissue damage, but the temporary cavity can also have devastating effects to surrounding tissues. Each area of the body is at risk for various and different injuries depending on the tract of the bullet, and emergency clinicians must be aware of the specific risks with each region of the body and be prepared to treat accordingly. The field of ballistics and the physics behind penetrating injuries is improving. Newer techniques, such as ballistic gelatin, are able to better explain the various injury patterns, allowing the treatment of these wounds to improve, based on evidence.