The transmission of data in digital form has long been known to offer many advantages over analogue transmission. Digital modulation is an outgrowth of the more familiar methods of analogue modulation such as amplitude, frequency and phase modulation. Recommendation ITU-R BT.1306 lists the important parameters of a DTTB modulation system and provides parameter values or ranges of values for those parameters. The Recommendation allows the system designer to tailor system performance to meet a variety of different design constraints. The modulation techniques proposed in the Recommendation are for either single or multiple carrier modulation methods and for different channel bandwidths – 6, 7 and 8 MHz options are available. This chapter explains some of the issues involved in selecting a suitable modulation system for a given application.