Abstract Absolute distance interferometry, which has been investigated and developed in various research laboratories worldwide and which can be regarded as an extension of conventional interferometry, offers the advantages of high resolution coupled with the fact that measurement operations suspended by an interruption of the laser light beam are resumed as soon as the shading disappears. Additional benefits accrue from the immediate availability of a distance value when the facility is activated and from the fact that point measuring operations can be conducted without complicated linear stages. An absolute interferometrical distance measurement technique using a tunable semiconductor laser which, by virtue of its external cavity, has extremely small linewidth and, therefore, considerable coherence length, is discussed in this contribution. The application of this technique has already permitted a relative measurement uncertainty of 10 −6 to be achieved over a distance of 40 m.