IEC 60601-2-66:2015 applies to the basic safety of hearing instruments and hearing instrument systems, hereafter also referred to as ME equipment or ME system. This second edition cancels and replaces the first edition published in 2012. It constitutes a technical revision to adapt IEC 60601-2-66:2012 to the technical corrections introduced by Amendment 1 (2012) to IEC 60601-1:2005, as well as to clarify and correct the wording of this particular standard and to implement minor changes requested by interested parties.