IEC 62366-1:2015+A1:2020 specifies a process for a manufacturer to analyse, specify, develop and evaluate the usability of a medical device as it relates to safety. This usability engineering (human factors engineering) process permits the manufacturer to assess and mitigate risks associated with correct use and use errors, i.e., normal use. It can be used to identify but does not assess or mitigate risks associated with abnormal use. This first edition of IEC 62366-1, together with the first edition of IEC 62366-2 (not published yet), cancels and replaces the first edition of IEC 62366 published in 2007 and its Amendment 1:2014. Part 1 has been updated to include contemporary concepts of usability engineering, while also streamlining the process. It strengthens links to ISO 14971:2007 and the related methods of risk management as applied to safety related aspects of medical device user interfaces. Part 2, once published, will contain tutorial information to assist manufactures in complying with Part 1, as well as offering more detailed descriptions of usability engineering methods that can be applied more generally to medical devices that go beyond safety-related aspects of medical device user interfaces. The contents of the corrigendum of July 2016 have been included in this copy. This consolidated version consists of the first edition (2015) and its amendment 1 (2020). Therefore, no need to order amendment in addition to this publication.