Research in advanced materials is continuously driving modern technologies forward. For example, semiconductors have laid the foundation for today's electronics industry. While constantly searching for new materials in nature, another approach is to craft novel composite materials beyond the naturally available properties. This is accomplished by directly designing the arrangement of the ‘atoms’ into a desired architecture or geometry, instead of chemical compositions in natural materials. This new type of artificial material is called metamaterial—a new frontier of science, which first emerged in the field of optics and photonics. In the past two decades, we have witnessed an explosion of the meta-concept, bending the fundamental rules of light. This consequently realized the full exploitation of dielectric and metallic properties in the permittivity–permeability plane, leading to unique optical effects, such as negative optical refractive index and superlenses. These intriguing light–matter interaction behaviors, enabled by metamaterials, provide the further prospect of new functional photonic technology. This technology has a strong impact on our life, ranging from highly integrated photonics circuits, energy-efficient light sources, sub-diffraction-limited optical imaging, environmental and healthcare sensing, etc.