For years, bioengineers and orthopedic surgeons have applied the principles of biomechanics to gain valuable information about the complex function of the anterior cruciate ligament (ACL), as well as to improve the design of replacement grafts for ACL reconstruction. New experimental tools, such as robotic testing systems and mathematical models have been used to measure the multiple degree-of-freedom (DOF) knee kinematics, in situ forces, and biomechanical properties of the ACL. This manuscript will review specific examples of how biomechanics has impacted surgical reconstruction of the ACL by improving technical factors such as graft selection, tunnel placement, initial graft tension, graft fixation, and graft tunnel healing. Evolution of the single-bundle ACL reconstruction to the more anatomical double-bundle reconstruction will be featured. Finally, the future role of biomechanics to facilitate in vivo data for further improvement of ACL reconstruction will be discussed.