Indentation is a popular method for evaluating mechanical properties of materials and structures, including elastic modulus, yield strength, hardening coefficient, residual stress, fracture toughness, and viscoelastic behavior, among others. It can also be applied to measure the properties of individual phases as well as global properties of composite materials, coatings and multilayers. Since it requires much less effort on sample preparation than other techniques, it is in particular useful for small material structures and biological materials (including living tissues). The primary challenge remains in the explanation of indentation data, since the material properties are implicitly related with indentation response; due to the finite local deformation involved and nonlinear contact conditions, computation modeling of indentation is an indispensable tool to correlate the indentation characteristics with material parameters, from which a reverse analysis can be carried out to identify material properties from indentation tests.