The FIRST survey is a long-term project whose completion is many years in the future. The area of sky covered by the FIRST survey will increase in increments of every 16 months. At the very least, then, the FIRST catalog of sources will grow with time. More confusing for the potential user, however, the catalog of sources for some particular region of the sky may change with a new release. This will be generally true for regions currently at the edge of the survey for which a previously constructed coadded image will be enhanced as new fields become available. Likewise, sources in the vicinity of internal gaps will change when the gaps are subsequently filled. In addition, source positions and flux densities can be expected to change at the one-sigma level as new data are added. At worst, some sources will disappear and others appear with new releases of the catalog as coverage gaps are filled and as we develop more sophisticated algorithms to exclude spurious sources. It is our intention to archive each release of the FIRST catalog so that researchers using a particular version of the catalog will have continuing access to that version. Instructions for accessing all FIRST data products are available via the FIRST homepage (http://sundog.stsci.edu).
The success of the FIRST survey is in large measure due to the generous support of a number of organizations. In particular, we acknowledge support from the NRAO, the NSF (grants AST-94-19906 and AST-94-21178), IGPP/LLNL, the STScI, NATO, the National Geographic Society (grant NGS No. 5393-094), Columbia University, and Sun Microsystems. We also thank Columbia undergraduates Ali Kinkhabwala, Beth Willman, and Gabe Perez-Giz for assistance in performing the comparisons of the FIRST catalog with the data from other wavelength regimes and with the Lehar high-resolution survey. This paper is Contribution Number 601 of the Columbia Astrophysics Laboratory.