Replication technology is playing an increasingly important role in the production of micro-optical elements and systems. Hot embossing, injection moulding and uv-embossing all can produce high quality optical elements in very cost-effective processes. The development of wafer scale replication technology using uv-curable sol-gel and polymer materials enables refractive and diffractive micro-optical elements to be replicated directly onto glass substrates or onto Si or III-V device wafers. New sol-gel materials allow the combination of replication with lithography to leave selected areas material-free for sawing and bonding. The technology is suitable for the production of both planar micro-optical elements and stacked optical microsystems. Replication techniques are inherently of very high resolution, so that optical nanostructures such as subwavelength structures can also be produced by the same technologies. Grating nanostructures with linewidths less than 100 nm have been replicated into polymer and sol-gel materials for the cost-effective fabrication of large area subwavelength structures for applications such as anti-reflection surfaces, polarisers and certain types of resonant filters.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.