Structural dynamics of machine tools causes deviations between the actual and NC programmed tool paths. These deviations, often negligible in traditional cutting, can become the major cause of errors in high speed machining. This paper presents new methods for: (1) model based assessment of the dynamic performance of machine tools, and (2) derivation of analytical models representing the structural dynamics. The assessment is accomplished by combining measurements obtained by means of the Heidenhain Cross Grid and multi-component, wide bandwidth accelerometers. The proposed performance assessment and modeling methods are illustrated by examples obtained for various machines at different feed speeds.