Human understanding of natural phenomena such as sound, light, electricity, and magnetism, and the use of the material effects of these phenomena enable us to understand the world and use the knowledge acquired to serve mankind. Smart materials or structures are gradually emerging that can sense the external environment and internal state changes. Smart structures and devices have been widely used in information technology, in new materials technology, and in high-tech fields such as aerospace; and increasingly show their great advantages. Smart devices often use functional materials such as piezoelectric/ferroelectric materials, ferromagnetic materials, and shape memory alloy (SMA) materials; and commonly work in the electricity-force-magnetism-thermal coupling load environment. The design of smart devices must consider the deformation, vibration, and instability of structural components and systems occurring in external magnetic fields, electric fields, and large temperature gradient environments. Their reliability is of great concern. The primary concerns of the mechanical properties of smart materials include the determination of the constitutive relations of anisotropic smart materials, the field analysis of multifield coupling, and the determination of basic mechanical parameters. This chapter introduces the basic concept of smart materials and the most widely used SMAs, magnetostrictive and ferromagnetic SMA materials, ferroelectric and piezoelectric materials, and their related mechanical properties.