Deep UV-induced modification of the refractive index of polymers is a useful technique for realizing integrated optical circuits for telecommunication and sensor applications. The combination with replication techniques such as hot embossing opens up a variety of possibilities such as a monolithic integration in optical or fluidic microsystems. In this article the fundamental understanding of the deep UV process is given including examples of fabricated waveguide based devices. (c) 2006 American Vacuum Society.