Wind farms are presently an important component of the world's source of electric energy from renewables. With the increasing size of wind turbine generators (leading to bigger wind farms), it has become essential for Transmission System Operators (TSOs) to be able to control, regulate and monitor wind farms like any other modern power plant. For this to be possible, suitable communication facilities are essential to allow the exchange of information between control, regulation, monitoring, visualization and data storage systems. A concise review is presented of the communications requirements and available technology for the Operation and Maintenance (O&M) of modern wind farms (either onshore or offshore).