The Lachman and the pivot shift are the two clinical tests most commonly used to assess instability in the anterior cruciate ligament (ACL)-deficient knee. Because it is quantifiable, the Lachman test has become the benchmark for assessing the success of ACL reconstruction. As a result, surgical techniques have been developed that effectively eliminate anterior laxity of the knee. Recent studies have shown, however, that rotational stability is not always restored after ACL reconstruction. Furthermore, there is mounting evidence that the pivot shift examination correlates with functional instability and patient outcomes better than does any other physical examination test. This test attempts to reproduce the functional combined rotary and translational instability in the ACL-deficient knee. Although the pathologic kinematics of the pivot shift are difficult to measure, recent technological advances have allowed more accurate and objective descriptions of the pivot shift, which have furthered our understanding of the complex motions involved. These advances may lead to a method of quantifying the pivot shift for research purposes and, ultimately, to ACL reconstruction that is tailored specifically to each patient's objectively measured rotational instability.