IEC 61400-24 is the part of the wind energy generation system series that deals with lightning protection. Wind turbines present a particularly severe lightning exposure: they are tall, sited in open terrain and often in coastal or mountainous locations with high lightning density, and their blades rotate, so the protective measures used on static structures cannot be applied unchanged. The standard quantifies the risk by defining lightning protection levels and the corresponding threat parameters, that is the peak current, charge, specific energy and rate of rise that the protection system must tolerate, and it applies these to each part of the turbine. It sets out the requirements for the blades themselves, where the receptors and the internal down conductor must carry the full current without damage to the composite structure; for the nacelle, tower and foundation, which must provide the main conducting path; and for the electrical and electronic systems inside, which are protected by coordinated surge protective devices on the power and control circuits. Testing methods for the verification of blade protection and of the electrical installation are included.