IEC 60601-1-2 is the collateral standard that governs electromagnetic compatibility for medical electrical equipment and medical electrical systems. It differs from general EMC standards in one important respect: compliance is not judged on emissions and immunity alone but on whether the equipment continues to deliver its basic safety and essential performance. The collateral standard therefore requires the manufacturer to identify the essential performance of the device, to define the electromagnetic environment in which it is intended to be used, and to demonstrate through test that no unacceptable risk arises within that environment. Separate requirements are given for the professional healthcare facility environment and for the home healthcare environment, the latter being considerably stricter for immunity. The document specifies the applicable emission limits and the immunity test levels for electrostatic discharge, radiated radio-frequency fields, electrical fast transients, surges, conducted disturbances, power frequency magnetic fields and voltage dips, and it defines the acceptance criteria in terms of the clinical function rather than a simple pass or fail. Labelling, instructions and the warnings that must accompany a device whose performance is affected are also regulated.