The anterior cruciate ligament is one of the four crucial ligaments that connects and stabilizes the femur and the tibia.The ACL runs diagonally in the middle of the knee on the anterior side this helps prevent the tibia from sliding out in front of the femur, it also provides rotational stability to the knee. Tearing the ACL is the most common type of knee injury, it is usually caused by cutting, pivoting, side stepping maneuvers, awkward landings, and collisions that result in unnatural movements. The short term effects of this injury are difficulties walking, major swelling of the knee, knee instability, loss of full motion, and tenderness of the bone. ACL tears are usually accompanied with the tearing of other knee ligaments or menisci. Long term effects of this injury if left untreated are knee instability (especially the ability to move the knee in lateral or rotational movements) which can cause the knee to slide and make a loud popping noise followed by swelling, possible arthritis due to the tibia and femur being unstable and rubbing off on surrounding materials, and the loss of full range of knee movement. ACL injuries can be identified through the use of MRI’s or Lachman’s test. Immediate treatment that would best help the injury would be to apply ice and compression to the injury accompanied with the use of a knee brace, elevation to the leg will also help reduce swelling. The only way to properly heal a ACL tear is through surgery as the dense connective tissue of the ligament will not heal naturally. Surgery is not suitable for everyone due to factors such as age, activity, and religion. The surgery to heal the ACL uses the users own patellar tendon for a replacement or a cadaver piece to replace the torn ligament. It takes the ligament six months to fully heal after surgery and this is with the accompaniment of rehab. Rehab of the this injury consists of constant stretching, cardio, and weight strengthening courses. This helps stretch and strengthen the tendon and strengthen surrounding muscles to give better stability and help prevent future injuries.