A medical device is any device intended to be used for medicinal purposes by physical actions.
MDR defines Medical device as: ‘’ any instrument, apparatus, implement, machine, appliance, implant, reagent for in vitro use, software, material or other similar or related article, intended by the manufacturer to be used, alone or in combination, for human beings, for one or more of the specific medical purpose(s) of:
- diagnosis, prevention, monitoring, treatment or alleviation of disease,
- diagnosis, monitoring, treatment, alleviation of or compensation for an injury,
- investigation, replacement, modification, or support of the anatomy or of a physiological process,
- supporting or sustaining life,
- control of conception,
- disinfection of medical devices
- providing information by means of in vitro examination of specimens derived from the human body;
and does not achieve its primary intended action by pharmacological, immunological or metabolic means, in or on the human body, but which may be assisted in its intended function by such means ‘’.

To better understand what a medical device is, we provide a shorter definition:
A medical device is any device intended to be used for medicinal purposes by physical actions (i.e., mechanically). It includes detection, diagnosis, and treatment of the disease, in-vitro, in-silico, or in-vivo. It means that in-vitro diagnostic (IVD) devices, such as test kids and reagents, and software, are also medical devices.
The definition applies to a wide range of products, from the simples (tongue depressor) to the most sophisticated (robotic surgery), all of them regulated by the MDR 2017/745. The regulation entered into force in May 2017 with a staggered transition period of 3 years. Due to COVID-19 pandemic, the transitional period was extended by one year, until 26 May 2021.
Several ISO standards apply to medical devices such as the ISO 14155 for the design, conduct, recording, and reporting of clinical investigations with medical devices in human subjects; the ISO 13485 for Quality Management; and the ISO 14971:2019 for risk analysis.
CE-mark is required to commercialize a medical device in the European Community. MDR Annex VIII and Council Directive 93/42/EEC classify the medical devices by risk:

The Declaration of Conformity shall state that the requirements specified in the MDR regulation have been fulfilled for the medical device. The Declaration of Conformity is verified by a Notified Body (except for class I self-certificated) who emits the Certification of Conformity.