This chapter has surveyed and reviewed the range of PTM techniques available for fibre transmission and outlined their advantages from the standpoint of bandwidth-efficient modulation of analogue-sourced signals. A general classification method has been described by which different members of the PTM family may be categorised. Equations have been presented to describe the modulation spectrum for each of the different methods. To explore the high frequency potential of PTM the interaction between distortion performance and minimum sampling ratio as a result of sidetone overlap has been examined. Calculations have indicated that, operating above threshold, SWFM could, for example, offer an improvement factor of almost 20 dB for a system restricted to a transmission channel bandwidth of 1 GHz operating with a maximum input signal frequency of 100 MHz.