Ongoing research focuses on improving the performance, adjustability, and integration of metamaterials and metasurfaces across the entire RF–optical spectrum. This book aims to unify dispersed device-level advances into a precise mechanism–function–application map, providing actionable pathways from principle to engineering for structured RF–optic fields using metamaterials and metasurfaces. By highlighting their recent advances and applications, this book provides the conceptual and technical foundation for research and design, clarifying their complementary roles in wireless communication systems.