This text provides a comprehensive description of the technical challenges inherent in wireless communications using diffuse infrared radiation. The potential for broadband data rates has sparked an explosion of recent research in wireless infrared communications. The focus is on the physical layer problem of establishing a robust point-to-point link. The author explores the fundamental limitations of the medium, identifies the dominant impediments to achieving high data rates, and proposes design strategies to counter them. The text introduces the reader to a wide range of topics, including optical design, multipath propagation, electronics design, modulation, and equalization. It should be a useful reference for both design engineers and communications theorists, and can also be used as a text for advanced courses on the subject.