What is the ACL and Where is it Located?

The Anterior Cruciate Ligament (ACL) is strong band of connective tissue that attaches the femur to the tibia. It attaches to the near front of the proximal tibial plateaux to the distal femur at the intercondylar  notch.  the picture below shows an example of this.

Image source 

What is the purpose of it?

Its main function is to prevent anterior translation of the tibia in relation to the femur.  In other words, it keeps the knee joint stable by preventing the lower leg from moving forward.  This is especially important when participating in sports that involves cutting and turning.

Image source 

If the ACL is not present the likelihood that the knee will give way and compromise sports performance are very high. The ACL also helps to control rotation.

(Bruckner and Khan, 2009)