Knowledge of the mechanisms of bicruciate lesions and dislocation of the knee enables analysis and classification in terms of injuries’ location and type, guiding surgery and facilitating assessment. Careful history taking and clinical examination shed light on the mechanism involved, but exact identification of the lesion further requires examination under anesthesia and static and dynamic X-rays and MRI, which together enable precise determination of lesion type and location. There are two types of mechanism: gaping, causing ligament tear; and translation, causing detachment. When a single mechanism is involved, the lesion is said to be “simple”. Simple gaping causes bicruciate lesions without medial, lateral or posterior dislocation. Simple translation causes pure anterior or posterior dislocation. Gaping and translation may also occur in combination, causing dislocation with peripheral tearing. There are two types of classification: descriptive, based on X-ray findings – i.e., static classification; and physiopathological, based on clinical and dynamic X-ray findings. MRI further explores ligament detachment and bone lesions that are inaccessible to clinical and conventional X-ray examination. Physiopathological assessment-based techniques enable surgical procedure to be refined, defining the surgical approach according to lesion location and differentiating between lesions requiring repair (tears) and those with a good likelihood of spontaneous healing (capsuloperiosteal detachment). The classification advocated here is largely inspired by that of Neyret and Rongieras, extended to include dislocation with single bicruciate ligament lesion. It covers peripheral lesions completely, specifying type (tear or detachment) and including all bicruciate lesions as well as dislocations.