Nanoindentation has become an increasingly popular method to determine the mechanical properties of both homogeneous and heterogeneous materials. Rocks are inherently heterogeneous and understanding their mechanical properties is of vital importance for relevant engineering applications. Due to its high precision and resolution in both force and displacement, nanoindentation can be utilized to extract the localized mechanical properties of individual grains. This review paper presents an overview of applications of nanoindentation techniques in various rocks, such as shale, coal, limestone, marble, sandstone and claystone. Apart from the conventional mechanical parameters, i.e., Young’s modulus and hardness, other parameters, such as fracture toughness, time-dependent creep and tensile strength can also be obtained using nanoindentation methods. Basic equations and parameters employed to obtain the above mechanical parameters are clearly explained. In addition, merits and demerits of previous nanoindentation studies are summarised and roadmap for future trends of nanoindentation in geomaterials are suggested.