The VLC system consists of the light sources introduced in Chapter 2 , the photodetectors introduced in Chapter 3 , and the spatial channel. The design of the VLC system mainly includes link configurations, system construction methods, and spatial channel analysis. This chapter focuses on the technical content of these aspects, it consists of various optical wireless links, the commonly used IM/DD (intensity modulation with direct detection) technology for constructing an optical wireless communication system, and it provides a detailed analysis for various noises characteristics in the spatial channel, theoretical upper limit on the transmission rate (i.e., Shannon’s theorem) in the spatial channel as well as the receiver SNR (signal-to-noise ratio). Finally, the multipath effect generated by reflections and plural sources during indoor ray transmissions is discussed.