Star Trek: The Original Series and its sequels built a world that was connected by an established history and in-universe decisions, the results of which you could see appear across each series airing at the time. While this helped link the TV shows, it wasn’t the only way the Star Trek series would connect together. Sometimes characters would cross from one show to another for appearances that would further tie the programs together and give us unforgettable crossover episodes.
Whether it was Klingons from The Original Series appearing on Deep Space Nine or a cameo by The Next Generation's Geordi La Forge on Voyager, the creative situations our characters often found themselves in during the science fiction franchise's run provided plenty of opportunities to bring familiar faces from other shows onto another program. Some cameos were more fleshed out than others and, like all types of episodes in the franchise, a few are more noteworthy than the rest. Here are the 11 in-universe crossover episodes I think stand out the most and deserve a second look all these years later.