Current statistics suggest that preventable medical error is a common cause of patient morbidity and mortality, being responsible for between 44,000 and 98,000 deaths annually, and resulting in injuries that cost between $17 billion and $29 billion annually. An important approach to tackling this problem is to apply system design principles from human factors engineering (ergonomics). By doing so, systems and equipment become easier for people to work with, ultimately reducing the frequency of errors. In particular, in the case of medical equipment, the design of the user interface can impact enormously on its successful use. In this chapter we consider some of the elements of good and bad medical equipment design, using examples drawn from the literature and elsewhere. The concept of ecological interface design is also discussed, and some practical design guidelines are provided.