This paper focuses on the various aspects of gear metrology as it relates to the inspection, measurement and assessment of involuted parallel axis cylindrical gears. Gear metrology needs to be employed to assure reliable gear performance and interchangeability. A description of the elemental prime variables affecting geometrical gear accuracy is provided along with an explanation of some intentional modifications. Several countries have issued standards specifying tolerances for controlling and classifying gear accuracy and the paper refers to those from the American Gear Manufacturers Association (AGMA), British Standards (BS) and West Germany (DIN). Some of the latest methods and the most modern equipment available to perform these measurements are described.