This introduction to volume 2.2 was where I first learned how Walter Koenig's surname was pronounced! Koenig talks about the show's incidental music here, but gets it slightly wrong. Typically the first 6-7 episodes produced in each season would have original scores, and the rest of the season would usually make use of those episodes' music where apt - although a few episodes later on in the season would get their own music composed if they needed something a little different - usually something more comedic, romantic, or evocative of a particular period setting. The episodes on volume 2.2 have some of the most recognisable music in the series. Gerald Fried's Vulcan themes from "Amok Time" were reused a lot, usually in connection with Spock. Fred Steiner's score for "Who Mourns For Adonais" was also heard a lot, oddly more in season 3. And of course Sol Kaplan's wonderful music from "The Doomsday Machine" provided the backdrop to just about every space battle in season 2, and was a huge influence on the music from Jaws - there's a couple of uploads here where people have put the Doomsday Machine music into the climax of Jaws to show just how much of an influence it was!