It's a collected volume of James Blish's adaptations of TOS episodes which were released in smaller paperback volumes from the late '60s well into the '70s. These were an absolute staple of Trek fandom at the time. There are noticeable differences in several of the adaptations, since in the earlier volumes Blish was working from early draft scripts of the episodes. He also did some of his own exposition which does not always jibe with later canon Trek. But I find that perfectly OK, since to me, TOS is the only Trek that counts.
While this collected volume is quite nice, I prefer the original paperbacks due to their fantastic cover illustrations, and because I love vintage paperback books.
Kor
Also worth noting the new B&N edition does not contain all the episode adaptations, just a selection.
I love vintage books too!