Fidelity is a fundamental concept for crucial decision-making processes during engineering design, test and evaluation of aircraft and rotorcraft. Fidelity, as applied to rotorcraft, proves to be a prerequisite for most human factors research and simulator development programs. This paper reviews the concept of fidelity, its metrics and methods concentrating on rotorcraft applications. The paper stems from the Applied Vehicle Technology (AVT) Panel of the NATO Science and Technology Organization (STO) work of NATO AV-296 concentrating on recent advancements on rotorcraft flight simulation model fidelity prediction and assessment. Starting from the question of what is meant with the term simulation fidelity, the paper will demonstrate that even though the term fidelity can be loosely translated as simulation goodness or faithfulness to reality, when it comes to fidelity assessment, this concept has a multidimensional and multifaceted character depending on the configuration considered. A key message of the paper is that simulation fidelity should be decomposed in different dimensions and attributes with their own metrics. Using multiple fidelity metrics is therefore meaningful for assessing simulation fidelity in general and in particular for the case of rotorcraft.@en