Due to the importance in clinical and cosmetic applications, the mechanical properties of skin tissue in vivo and in vitro have been studied extensively. In this paper, we present a comprehensive review on the recent developments of skin mechanics. The methods and apparatus of experiments in vivo and in vitro are summarized. The main mechanical properties and their anisotropy are reviewed, which includes Young's modulus, Poisson ratio, compressibility, strength, toughness, initial stress/tension, thermal expansion coefficient, binding force/delamination energy, and skin friction coefficient. Data from the literature are grouped and tabulated. Finally, future research directions in special areas are discussed.