The communication facilities of Santa Catalina Island are described with special reference to the radio telephone service to the Californian mainland and the mode of connection to the wire telephone networks at the ends of the radio telephone channel. The radio telephone link is full duplex, and is connected thru special two-way repeaters to the telephone system at each end. A simultaneous duplex radio telegraph channel is available. A number of special points are discussed, such as the narrowing, by means of filters, of the side frequency bands due to modulation, the circuits of the transmitter and receiver, automatic alarm systems indicating when any portion of the radio equipment ceases to function, thru signaling system, location, and antenna and ground arrangements. The service rendered is analyzed and the results of transmission measurements are given.