The Abell catalog of rich clusters of galaxies is an all-sky catalog of 4,073 rich galaxy clusters of nominal redshift   z ≤ 0.2. This catalog supplements a revision of George O. Abell’s original “Northern Survey” of 1958, which had only 2,712 clusters, with a further 1,361 clusters – the “Southern Survey” of ****, published after Abell's death by co-authors Harold G. Corwin and Ronald P. Olowin from those parts of the south celestial hemisphere that had been omitted from the earlier survey.