IEC 61400-1:2019 specifies essential design requirements to ensure the structural integrity of wind turbines. Its purpose is to provide an appropriate level of protection against damage from all hazards during the planned lifetime. This document is concerned with all subsystems of wind turbines such as control and protection functions, internal electrical systems, mechanical systems and support structures. This document applies to wind turbines of all sizes. For small wind turbines, IEC 61400-2 can be applied. IEC 61400-3-1 provides additional requirements to offshore wind turbine installations. This document is intended to be used together with the appropriate IEC and ISO standards mentioned in Clause 2. This edition includes the following significant technical changes with respect to the previous edition:a) general update and clarification of references and requirements;b) extension of wind turbine classes to allow for tropical cyclones and high turbulence;c) Weibull distribution of turbulence standard deviation for normal turbulence model (NTM);d) updated design load cases (DLCs), in particular DLC 2.1 and 2.2;e) revision of partial safety factor specifications