Monitoring the human body is a key element of digital health science. Low-cost sensors derived from smartphones or smartwatches may give the impression that sensors are readily available; however, to date, very few of them are actually medical devices. Designing medical devices requires us to undertake a specific approach demanding special skills, as it concerns the integrity of the human body. The process is tightly framed by state regulations in order to ensure compliance with quality assessment, risk management and medical ethics requirements. This book aims to give biomedical students an overview on medical devices design. It firstly gives a historical and economical approach, then develops key elements in medical device design with reference to EU and US regulations, and finally describes sensors for the human body. The clinical approach is presented as the central element in medical device qualification and this offers a perspective on the use of numerical simulation, particularly since its continued growth in the USA; despite the fact that the approach is strictly limited by regulations.