A medical device is an instrument, machine, implant, or other similar article and intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease, which does not achieve its primary purpose through chemical action within or on the body and which is not dependent upon being metabolized.  

Medical devices include products used for treatment as well as diagnostic products. Pacemakers, surgical lasers, wheelchairs and orthopedic pins are all examples of medical devices used in treatment. Examples of diagnostic medical devices range from pregnancy tests to magnetic resonance imagining (MRI) systems.