Ultra wideband (UWB) is a very promising communications technology under active research, development, regulation, and standardization efforts, with applications in computer and communications, consumer, radar, automotive, and cable communications. Impulse radio (IR) is an UWB modulation that uses waveforms that consist of trains of time-shifted sub nanosecond pulses. Data is transmitted using pulse position modulation at a rate of many pulses per symbol. Multiple access capability is achieved using spread spectrum time hopping. The IR-UWB promises to be a viable technique to build relatively simple and low-cost, low-power transceivers that can be used for short range, high speed multiple-access communications over the multipath indoor wireless channel. In this book we study the performance of IR-UWB under different scenarios. First, we provide an overview of the research, development and regulations efforts related to IR-UWB. Secondly, we include examples of signal design and an assessment of the performance of IR-UWB in the presence of noise, multipath, and multiple access interference. Finally, we discuss some of the tradeoffs between performance and receiver complexity.