Metamaterials are a type of artificial material with microstructural features that are characterized by physical properties not found in nature. Metamaterials originated in the field of electromagnetics and have now blossomed in fields such as acoustics, mechanics and optics. Negative Poisson’s ratio (NPR) metamaterials are common mechanical metamaterials, also called auxetic metamaterials, that have a long development history and are widely known for their tension-expansion and compression-contraction deformation behavior. In this chapter, we reported the development history of mechanical metamaterials, revealed the NPR effect and deformation mechanism, and discussed the applications in three aspects. Most importantly, three kinds of new auxetic metamaterials were introduced, i.e., lightweight and high-strength auxetic metamaterials, multi-step deformation auxetic metamaterials and artificial intelligence auxetic metamaterials. For every topic, the current and future development potentials are given, especially the fabrication process of composite for lightweight and high-strength auxetic metamaterials. This content will help people understand the concept of auxetic metamaterials and continue to conduct new research based on it.