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Reliable and accurate indoor positioning for moving users requires a local replacement for satellite navigation. An UltraWideBand (UWB) system is particularly suitable for such local systems, including temporary installations supporting emergency services inside large buildings. The requirements for emergencies will be very variable, but will generally include: good radio penetration through structures, the rapid set-up of a stand-alone system, tolerance of high levels of reflection, and high accuracy. The accuracy should be better than 1 m, as sometimes it matters which side of a door you are, and locations should be in 3 dimensions. Support for robots as well as people would call for still better accuracy. Rapid set-up implies very little surveying of the fixed terminals, and positioning relative to the mobile and fixed terminals. A radio system that measures ranges between fixed and mobile terminals matches these requirements, but the requirements for accuracy and for dealing with multipath need a bandwidth of more than 1 GHz. Thus UWB is the preferred solution, as it has the specific advantage of high accuracy, even in the presence of severe multipath. This paper presents the features and system design options for UWB positioning systems, and shows how they match the indoor location demands of emergency services. The main features that are covered are: the deployment of terminals (how many, and where), the minimum requirements for fixed terminal surveying, integration (hybridisation) with GNSS, and solving for position inside the network. The main system design options are: whether the mobile terminals are transceivers or solely receivers, the UWB signal design and frequency span, and the use of the same signal for communications. The paper includes results from a demonstration UWB indoor positioning system being built at TRT (UK).