The Ninth Catalogue of Spectroscopic Binary Orbits continues the series of compilations of spectroscopic orbits carried out over the past 35 years by Batten and collaborators (see e.g. Cat. V/64). The catalogue is continuously updated, see http://sb9.astro.ulb.ac.be/ This version is dated 02-May-2011. Previous versions may be found in subdirectories "v00" (April 2005), "v01" (September 2005), etc...