Montage is a software toolkit used in astronomy to assemble astronomical images in Flexible Image Transport System (FITS) format into custom, science-grade image mosaics for the purpose of conducting astronomical research, as well as creating very large images for posters and other printed displays. The software won a NASA Space Act Award in 2006. The toolkit can be downloaded from the Montage Web site. A Montage Web service creates mosaics on-request from three all-sky survey data sets: 2MASS, DSS and SDSS. Montage was funded by the National Aeronautics and Space Administration’s Earth Science Technology Office, Computational Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology. The Web service uses software developed by the Infrared Processing and Analysis Center (IPAC) for the U.S. National Virtual Observatory, sponsored by the National Science Foundation.