**Abstract**

Metamaterial is the artificial structure under sub-wavelength dimension and could be designed to manipulate the electromagnetic wave radiation across the broad frequency range through microwave to much higher frequency, such as terahertz and optical regime. Lens antenna can generate the focused beam with high gain and shrink the bulky refractive body and feeds into a shape of flat form. This chapter will discuss the general concepts of metalens and the technology of metalens-based antenna at microwave, terahertz and optical frequency. The recent progress in the research and development of metalens antennas is reviewed with designs principle and typical applications. At last part, some innovative techniques such as dynamic focus-tuning of metalen are discussed in details.

**Keywords:** Microwave metalens antenna; Terahertz metalens, Optical metalens, achromatic metalens, metamaterial absorber
