Medical Informatics comprises the theoretical and practical aspects of information processing and communication, based on knowledge and experience derived from processes in medicine and healthcare. The processing takes place within computers ranging from large supercomputers for research, high performance work stations for image processing and retrieval to smart phones which support mobility and pervasive health applications. A variety of Operating Systems are used, dominated by Microsoft and Linux. The latter promotes an ‘open source’ approach, which is favoured by many in health. In today's ‘connected health’ paradigm, end-user devices are linked to hospital servers, each other and the Internet. This requires knowledge and understanding of security considerations which are important in this disciple, due to the ethical dimension of healthcare. In this section we study the use of a web based system to facilitate rehabilitation of people with Stroke. This can be classified as an eHealth application, and is an exemplar of the self management paradigm, which is set to become more important due to the ageing society and associated prevalence of chronic disease.