J/AJ/160/271 A catalog of ~30000 galaxies with ALFALFA-SDSS (Durbala+, 2020) ================================================================================ The ALFALFA-SDSS galaxy catalog. Durbala A., Finn R.A., Odekon M.C., Haynes M.P., Koopmann R.A., O'Donoghue A.A. =2020AJ....160..271D ================================================================================ ADC_Keywords: Galaxies; Photometry, RI; Photometry, G band; Extinction; Colors Keywords: Galaxies ; Late-type galaxies ; Galaxy evolution ; Sky surveys ; Astronomy databases Abstract: We present a HI optical catalog of ~30000 galaxies based on the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey combined with data from the Sloan Digital Sky Survey (SDSS). Our goal is to facilitate the public use of the completed ALFALFA catalog by providing carefully determined matches to SDSS counterparts, including matches for ~10000 galaxies that do not have SDSS spectra. These identifications can provide a basis for further crossmatching with other surveys using SDSS photometric IDs as a reference point. We derive absolute magnitudes and stellar masses for each galaxy using optical colors combined with an internal reddening correction designed for small- and intermediate-mass galaxies with active star formation. We also provide measures of stellar masses and star formation rates based on infrared and/or ultraviolet photometry for galaxies that are detected by the Wide-field Infrared Survey Explorer and/or the Galaxy Evolution Explorer. Finally, we compare the galaxy population in the ALFALFA-SDSS sample with the populations in several other publicly available galaxy catalogs and confirm that ALFALFA galaxies typically have lower masses and bluer colors. Description: The Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey provides HI 21cm line measurements for ~31500 galaxies over nearly 7000deg^2^ on the sky, out to a redshift of about 0.06. Exploiting the large collecting area of the Arecibo 305m antenna and the seven-beam ALFA radio camera, ALFALFA mapped ~6600deg^2^ of high galactic latitude sky in spectral line mode, covering a 100MHz bandwidth corresponding to 2000