The chapter presents current trends in the stiffness modelling of robotic manipulators. It provides an analytical literature review on the existing stiffness modelling approaches and their application to robotic manipulators. Particular attention is paid to the problems of stiffness modelling under external loading and stiffness modelling for the manipulators with closed loops and passive joints. As a summary of this chapter, open questions and current challenges in the stiffness modelling of robotic manipulators are highlighted.