Underwater wireless communications is a research field focused on the transmission and reception of data between submerged devices without physical connections. It investigates the unique properties of underwater communication channels, including acoustic, optical, and radio frequency propagation, and develops methodologies for reliable and efficient data exchange despite challenges such as high attenuation, limited bandwidth, multipath interference, and ambient noise. This field is critical for enabling applications ranging from environmental monitoring and resource exploration to autonomous underwater navigation and defense systems.