This chapter focuses on the mechanical aspects of tumor growth. After describing some of the main features of tumor growth and in particular the phenomena involving stress and deformation, the chapter deals with the multiphase framework recently developed to describe tumor growth and shows how the concept of evolving natural configurations can be applied to the specific problem. Some examples are then described according to the type of constitutive equation used, specifically focusing on contact inhibition of growth, nutrient-limited avascular growth, and interaction with the environment