The need for human tissues and organs has increased over the past few years, mostly because of population growth. The risks for transmission of contagious diseases have also imposed serious restrictions to the availabiliry of human transplants. Recent advances in tissue and organ engineering have generated much interest among cIinicians and patient sin various fields of medicine. This modern approach has already shown successful results with human skin substitutes ail over the world. This chapter is dedicated to ligament and tendon bioengineering. The technical approach developed to produce a human anterior cruciate ligament (ACL) substitUte is described. This methodology may eventually be adapted to produce other ligaments or tendons in culture. A bioengineered ACL (bACL) was developed by seeding human ligament fibroblasts in a hydrated collagen matrix. Our bACL is anchored with tWo bones, because bone-to-bone insertion is reported asthe most secure method for ligament fixation. The ACL substitUte is a good tool to stUdy connective tissue repair and the environmental and cellular factors that can affect collagen alignment and cross-linking in vitro. Ir may also become a therapeutic alternative for tom ACL replacement. The effects of cyclic stretching on the histologic featUresof the bACL are also described. Mechanical stimuli represent one of several concepts to explore in order to optimize bioengineered tissues. Our findings may also be useful to readers involved in the fields of orthopedies and physical therapy. Histologic analyses of bACL cultUred under cyclic traction revealed that fibroblasts are surrounded by bundles of collagen fibers organized in a wavy pattern, comparable to histologic features of native ACL. These results suggest that mechanical stimuli have an important impact on the evolution of bioengineered tissue-in vitro.