sci Astronomers often need to relate positions on an image of the sky to positions on the real sky to identify catalogued objects in images, tell other people where to look to find an identified object, or to compute motions of planets, satellites, asteroids, or comets. WCSTools is a package of programs and a library of utility subroutines for setting and using the world coordinate systems (WCS) in the headers of the most common astronomical image formats, FITS and IRAF .imh, to relate image pixels to sky coordinates.