Background: Lengthening of the gastrocnemius-soleus complex is frequently performed for equinus deformity. Many techniques have been described, but there is uncertainty regarding the precise details of some surgical procedures. Methods: The surgical anatomy of the gastrocnemius-soleus complex was investigated, and standardized approaches were developed for the procedures described by Baumann, Strayer, Vulpius, Baker, Hoke, and White. The biomechanical characteristics of these six procedures were then compared in three randomized trials involving formaldehyde-preserved human cadaveric lower limbs. After one of the lengthening procedures was performed, a measured dorsiflexion force was applied across the metatarsal heads with use of a torque dynamometer. Lengthening of the gastrocnemius-soleus complex was measured directly, by measuring the gap between the ends of the fascia or tendon. Results: The gastrocnemius-soleus musculotendinous unit was subdivided into three zones. In Zone 1, it was possible to lengthen the gastrocnemius-soleus complex in either a selective or a differential manner?i.e., to lengthen the gastrocnemius alone or to lengthen the gastrocnemius and soleus by different amounts. The procedures performed in this zone (Baumann and Strayer procedures) were very stable but were limited with regard to the amount of lengthening achieved. Zone-2 lengthenings of the conjoined gastrocnemius aponeurosis and soleus fascia (Vulpius and Baker procedures) were not selective but were stable and resulted in significantly greater lengthening than Zone-1 procedures (p <0.001). In Zone 3 (Hoke and White procedures), lengthenings of the Achilles tendon were neither selective nor stable but resulted in significantly greater lengthening than Zone-1 or 2 procedures (p <0.001). Conclusions: Surgical procedures for the correction of equinus deformity by lengthening of the gastrocnemius-soleus complex vary in terms of selectivity, stability, and range of correction. Procedures for the correction of equinus deformity have different anatomical and biomechanical characteristics. Clinical trials are needed to determine whether these differences are of clinical importance. It may be appropriate for surgeons to select a procedure involving the zone best suited to the clinical needs of a specific patient. Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.