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This is sometimes also called "Star Trek: The Animated Series" or "Star Trek: The Animated Adventures," but its proper title is simply "Star Trek." It is an animated continuation of the live-action series Star Trek (albeit with half hour episodes, rather than hourlong episodes). The original series, of course, aired from 1966-69, while the animated series aired from 1973-74. I believe it used scripts originally intended for the first series, and had other scripts written by the same people who wrote for that show, as well as voices provided by the original cast (though Chekov was absent). Also, there were a couple of new recurring characters: a Caitian named M'Ress, and an Edosian named Arex, though they're used perhaps a bit less than I would've liked, especially M'Ress. The main cast provided a lot of voices for guest characters, as well.
Some of the animation, I mean the actual drawing, was decent, especially backgrounds. And the characters certainly looked good enough, though their movement was kinda lame. Also I thought the stories were often kind of silly, not quite as good as the original series... but then again, I'm sure the stories must've been a good deal better than the other cartoons of the time, and besides, the live-action series could be a bit silly, itself, at times. Anyway, I'm pretty sure most people consider the animated series to be canonical within the Star Trek universe. And there really were some decent stories. Not sure what else to say....