Skin tightening is one of the cornerstones of skin rejuvenation and is defined as the improvement of skin laxity and crepiness of the skin. There are several energy-based devices that can produce significant skin tightening without surgery, both on and off the face. The mechanisms of skin tightening involve collagen denaturation resulting in collagen shrinkage and tissue tightening, and the wound healing response that generates new collagen and elastin. These hypothesized mechanisms of skin contraction leading to clinical skin tightening have been derived from histological, immunohistochemical, and electron microscope analysis, as well as in vitro and in vivo experiments. This review is aimed at evaluating and analyzing the literature on the proposed mechanisms for skin tightening by minimally invasive energy-based technologies.