Nanometrology is defined here as the science of measuring the dimensions of objects or object features to uncertainties of one nanometer or less. Four major tasks of nanometrology are examined: realizing a metric in the measurement space; establishing the metric in a coordinate reference frame; generating and measuring repeatable motion relative to the coordinate reference frame; and linking the testpiece to the coordinate reference frame/metric by a probe. Optical scales, x‐ray interferometry, heterodyne interferometry, Fabry–Perot etalons, impedance‐based transducers, and STM scales are evaluated as possible means to realize a metric. The major error sources, practical limitations, and guidelines for establishing a coordinate reference frame are described. The repeatability of sliding bearings and flexure bearings is examined and this combined with cosine and Abbe´ offset errors is used to estimate uncertainties in generating and measuring linear motion. Finally, the effects of probe geometry, probe interaction lengths, probe forces and probe energies on lengths measurements are discussed. The paper concludes with estimates of an overall uncertainty for dimensional measurements of objects or object features up to 50 mm×50 mm in size when using optical microscopes, electron microscopes, and STMs as probes.