Today’s wind turbines are getting ever bigger in size,making the design and the development more complicated while the safety factors are very often being reduced to the allowed minimum limits in order to keep the design economic competitive.While the structural analysis meanwhile has reached a mature level in the industry and is considered in the design,the dynamic analysis of the drive train and its components is not investigated comprehensively.Anyhow,the detailed knowledge of this dynamic behaviour is of major importance for the evaluation of the design loads for the machinery components.Thus the detailed analysis of the dynamic behaviour is a mandatory part of the certification of wind turbines according to most standards or guidelines in order to investigate load-increasing resonances in the main drive train components.Since these resonance phenomena are usually not represented in the global simulation model for the determination of the design loads a separate analysis is required in most cases.This separate analysis requires a simulation of a more detailed drive train model representing all the drive train components in such a way that relevant mode shapes and eigenfrequencies can be identified and evaluated properly.At the time being,detailed requirements and guidance for this kind of analysis can only be found in the “Guideline for the Certification of Offshore Wind Turbines” and “Guideline for the Certification of Wind Turbines” by Germanischer Lloyd Industrial Services GmbH,Renewables Certification (GL).The latest revision of this Guideline was issued in 2012 (offshore) respectively in 2010 (onshore).This paper shares the authors’ experience in the assessment of these dynamic analyses in the course of certification.By pointing out the most common problems and questions as well as explaining the general requirements for these analyses the paper gives the reader a general understanding of this topic.