We live in a world of information, and emerging technologies, which compel us to look for new ways to collect, process, and distribute information. Today we are faced with an information overload problem as users struggle to locate the right information in the right way at the right time. In my view this is an “overload” of trivial information coupled with a gap in access to important information. Digitization of information and communications has seen the rise and rise of computers to a now ubiquitous position in our society. However, the problem remains as to how to merge the digital world with sensing, and respond to changes in the real world. Ubiquitous information systems are needed that will automatically sense and importantly, respond to changes in their environment and usage in order to deliver a more intelligent, proactive and personalized information service. These systems may be wearable, enabling them to disappear into our personal space, enhancing rather than burdening our daily activities. Conventional sensors are generally unsuitable for wearable body monitoring devices either due to their physical structure or their functional requirements. This thesis examines this area of wearable sensors, detailing the development and characterisation of novel sensing materials and outlines their performance in various on-body monitoring applications.