ESDU 97016 summarises several drag estimation methods as illustrative examples of the range of techniques and the levels of sophistication that exist. The methods rely on the summation of contributions due to particular airframe components or flow mechanisms. The discussion includes consideration of datum conditions, the use of simple sweep rules and strip theory in calculating wing profile drag, a brief consideration of excrescence, interference and propulsion system contributions, and the treatment of trailing vortex, wave and longitudinal trim drag. Those contributions that should, ideally, be considered are itemised in a Reference Scheme that sets the format and notation for a group of tables that provide the illustrative examples. These examples range from the relatively simple to those that require at least some usage of Computational Fluid Dynamics techniques. A table lists all ESDU documents that can be used to estimate the drag components. ESDU 81026 considers the representation of airframe drag for performance calculations and gives detailed examples of individual aircraft drag characteristics.