This chapter provides mechanical properties of polymeric materials. Relaxational and destructive process, fracture mechanics, quasistatic testing and transient testing, impact behavior, viscoelasticity and dynamic mechanical testing of polymeric materials are explained. As a result of the processing procedures used, plus handling in transport, etc., polymeric materials and components exhibit structure imperfections at various levels. Stress concentration factor, stress intensity factor, crack propagation, shear yielding along with Griffith’s Theory of Fracture are explained. The quasistatic method involves slow loading in which tension, compression and flexure belongs. The quasistatic methods have to be distinguished from so-called transient tests which include stress relaxation and creep. Specimens for testing may be produced by processing operations such as injection molding, compression molding, or machining from sheets. Tensile testing is the most frequently used method to characterize the material strength. Viscoelasticity of polymers represents a combination of elastic and viscous flow material responses. Dynamic mechanical analysis (also called dynamic mechanical thermal analysis) enables simultaneous study of both elastic and viscous flow types of behavior. The mechanical behavior of the elastomer is studied as a function of temperature. In addition, the chapter tabulates the mechanical data for most often used polymers.