Ion exchanged devices have been extensively studied at LEMO for twenty years and this work has shown the numerous advantages of this low-cost efficient technology based on the exchange of some alkali ions of a glass substrate with the ones of a molten salt. In this paper, the basics of ion exchange technology is first presented, then the use of various ions couples is discussed in terms of waveguide characteristics and technological trade-offs. The second part of the article is focused on three different application fields of ion exchanged devices which each emphasis a precise advantage of this technology: sensors, astronomy and telecommunication. Concerning the sensors, a low cost integrated displacement sensor is shown, its accuracy is better than 20 nm at a distance of 5 m. In the case of astronomy, results on a two telescopes interferometer recombining head are presented. Because of the large spectral bandwidth of ion exchanged waveguides, fringe contrasts up to 80 percent were measured. As an example of a telecommunication device, narrow emission linewidth integrated DFB lasers realized on rare earth doped substrate are treated. Finally, a presentation is made on some possible evolutions of the ion exchange technology such as hybridization with polymers or ion exchange in thin films.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.