This Second Edition of the Concise Catalog of Deep-sky Objects is a thorough primer for the curious amateur astronomer who is interested in understanding the astrophysical nature of the most observed deep sky objects. Equally valuable when used as background reading or at the telescope eyepiece, the book enables amateur astronomers to enhance their viewing experience by gaining a better understanding of the objects that they are observing. The past decades have seen an unprecedented increase in our understanding of objects commonly observed by amateur astronomers. Much of this growth is the result of experimental data obtained with a new generation of professional telescopes. However, most of this professionally generated information is contained in journals that most amateur astronomers either do not have access to or would find difficult to read. At the same time the advent of affordable, mass-produced, good-quality telescopes and astrophotography equipment in addition to affordable,