This is another of several STAR TREK factual books published during the 1970s, years after the show had crashed off NBC but during the first blooming of the post-cancellation fandom that - by the end of the decade - propelled the (soon-to-be) franchise onto the big screen.
Gerrold's THE TROUBLE WITH TRIBBLES is the episode everyone remembers. And with good reason. It adeptly demonstrates how the show (and its cast) could with gears from SF adventure to comedy... and still be gripping entertainment.
This is the behind-the-scenes story of that story, penned by Gerrold himself. As far as I know, it's been out-of-print for decades which is a bit surprising considering, at its peak, how many Trek-related publications were vying for retailer space. These days... you're lucky to see one non-fiction book a year.