Metasurfaces are a class of artificial electromagnetic structures composed of subwavelength arrays of scatterers or antennas. These structures can manipulate the phase, amplitude, and polarization of electromagnetic waves in a highly controllable manner, leading to a wide range of applications in optics, telecommunications, and sensing. Metasurfaces can be designed to achieve functionalities such as flat lenses, holograms, metasurface-based antennas, and beam steering devices, among others. Research in metasurfaces is focused on developing novel design techniques, fabrication methods, and applications for these versatile and compact devices.