Characteristics of silicon photonic integrated circuits that have enabled their inclusion in digitial communication systems are discussed. Frequencies and wavelengths of operation of microwave and optical/infrared systems of interest are defined. The uses of optical components in microwave systems are motivated and demonstrations of such microwave optical systems are reviewed. The literature that discusses silicon photonic devices for generation, shaping and processing of microwave signals is overviewed. Microwave photonic applications in which components developed for digital communication can serve as building blocks are discussed.