Metasurfaces have become a rapidly growing field of research in recent years due to their exceptional abilities in light manipulation and versatility in ultrathin optical applications. They also significantly benefit from their simplified fabrication process compared to metamaterials and are promising for integration with on‐chip nanophotonic devices owing to their planar profiles. The recent progress in metasurfaces is reviewed and they are classified into six categories according to their underlying physics for realizing full 2π phase manipulation. Starting from multi‐resonance and gap‐plasmon metasurfaces that rely on the geometric effect of plasmonic nanoantennas, Pancharatnam–Berry‐phase metasurfaces, on the other hand, use identical nanoantennas with varying rotation angles. The recent development of Huygens' metasurfaces and all‐dielectric metasurfaces especially benefit from highly efficient transmission applications. An overview of state‐of‐the‐art fabrication technologies is introduced, ranging from the commonly used processes such as electron beam and focused‐ion‐beam lithography to some emerging techniques, such as self‐assembly and nanoimprint lithography. A variety of functional materials incorporated to reconfigurable or tunable metasurfaces is also presented. Finally, a few of the current intriguing metasurface‐based applications are discussed, and opinions on future prospects are provided.

Metasurfaces, the two-dimensional counterpart of artificial metamaterials, have attracted much attention because of their exceptional ability to manipulate the electromagnetic wave such as amplitude, phase, polarization, propagation direction, and so on. Different from conventional lenses, metalenses based on the metasurface optics are truly flat and compact and exhibit superior performance. In this report, recent progress in the development of metalenses is explored. First, the working principle and characteristics of metalenses are discussed. Then, it is described how the dispersion aberration in metalenses can be eliminated to make them suitable for being employed in a range of applications that are difficult or impossible for traditional lenses. In addition, various metalens-based applications are introduced, including imaging, high spectral resolution spectroscopy, and multiplex color routing. Furthermore, a survey of reconfigurable and tunable metalenses is conducted. Finally, the report concludes by addressing future prospects of metalenses.

Integrated‐resonant units (IRUs), incorporated with multiple resonators into one building block or one resonator with multiple modes, show a great capacity for achieving controllable smooth and linear phase dispersion as well as amplitude manipulation over a continuous and broad bandwidth. Based on an IRU library designed in the wavelength range of 400 to 667 nm, three achromatic deflectors showing constant steering angles of 9.5°, 19°, and 28°, respectively, are numerically validated. Achromatic metalenses with various numerical aperture (NA) values are further experimentally demonstrated, displaying an unvaried focal length throughout the bandwidth of 420–650 nm (≈50% bandwidth to the central wavelength). The focusing efficiency of the achromatic metalens with NA = 0.124 achieves 26.31%, 19.71%, and 20.37%, respectively, at wavelengths of 420, 550, and 650 nm. In addition, a multi‐nanorod IRU design is numerically optimized to achieve above 50% conversion efficiency from visible to near‐infrared (400–1400 nm). Such IRU design is then employed to construct a versatile polarization convertor, generating six different polarization states simultaneously upon one linear‐polarized illumination. The IRU approach with broadband control of amplitude and phase response provides an unprecedented platform in realizing multifunctional full‐color metadevices.