The original series, Scooby-Doo, Where Are You!, had 25 episodes. Those episodes comprise the show’s two original CBS seasons, broadcast in 1969 and 1970.
The first season contained 17 episodes, beginning with “What a Night for a Knight,” while the second season added 8 more. Together, those seasons created the classic format: Fred, Daphne, Velma, Shaggy, and Scooby-Doo investigated apparently supernatural mysteries that usually ended with a human culprit in disguise.
Counting can become confusing because later broadcasts and home-video packages used the same title for additional material. A 1978 group of 16 episodes from other Scooby-Doo productions was later marketed as a third season, bringing some listings to 41 episodes. That expanded figure does not describe the original 1969–1970 run, which is conventionally counted as 25 episodes.