Electromagnetic metamaterials are artificial structures composed of periodically or aperiodically arranged sub-wavelength units. They have extraordinary media parameters that do not exist in traditional materials or are difficult to achieve with traditional technology， and can control electromagnetic waves in sub-wavelength scale. Metamaterials are closely related with materials， structures， and functions and hence go far beyond the concept and scope of traditional materials. They have been investigated throughout the fields related to “waves”， including electromagnetic， acoustics， mechanics， heat， quantum， etc. In the past two decades， electromagnetic metamaterials have been an international frontier research hotspot in the field of physics and information， and the related technologies derived from them have also produced a series of applications with significant effects in many fields， such as wireless communication， radar， imaging and so on.