A proper knowledge of the mechanical and material properties of biomaterials is a necessity in all medical device technologies: from tissue engineering to prosthesis design. In many cases, the design of novel biomaterials is governed by the mechanical properties and their characterisation may become a crucial factor in determining the success of a product. This chapter discusses the basic concepts of the characterisation and testing of materials. Starting from the fundamental concepts of elastic, viscoelastic and plastic deformation, an introduction to experimental methods is given. The special limitations and requirements set by biomaterials are discussed.