This document provides information regarding concepts and principles that underlie the IEC 60601 series of standards. (The IEC 60601 series is defined in the Introduction.) This document is intended to clarify and to point out the importance of the series as well as to provide guidance to understanding and to implementing the series. A consensus report (CR) is a publication of the Association for the Advancement of Medical Instrumentation (AAMI) developed to provide concise, prompt and practical guidance on narrowly focused topics of high importance to the health technology community.