The ACL fails to heal after injury. One of the reasons proposed in the past has been that the ACL cells are somehow incapable – that they cannot perform the basic biological processes required for wound healing. As we have seen in Chap. 6, some of these required processes include functions like cell migration into the wound site, cell proliferation within the wound site, collagen production, and nerve and blood vessel ingrowth into the healing tissue, all of which requires the formation of a provisional scaffold (i.e., clot) to provide the foundation to initiate wound healing. To work on determining which of these processes may fall short in ACL healing a series of studies were conducted and are summarized here. In contrast to previous work, these studies found that the ACL has a relatively productive response to injury. The cells within and around the tissue are capable of migrating into the wound site, are able to proliferate within the wounded tissue, and are capable of producing collagen and other extracellular matrix molecules. However, for the torn ACL, there is no provisional scaffold seen to bridge between the two tissue ends. This may be a key mechanism behind the failure of the ACL to heal and will be discussed in more detail in Chap. 8.