Season 21

Season 21 of premiered on PBS on Tuesday, October 24, 2017 with "Binky's 'A' Game/Brain and the Time Capsule" and "The Master Builders". Certain stations kicked off the season Monday, October 23, with Arthur and the Haunted Tree House, but others did not consider it part of the regular TV season. The season concluded on February 15, 2018 with "Invasion of the Soccer Fans/Pal and the Big Itch".

Production began on September 9, 2015. This is the second season where the animation is entirely done by Oasis Animation, though it was produced at the same time as Season 20. Together with Season 20, there are 14 new 30-minute episodes. There are also two one-hour specials that are not considered part of either season, though "Arthur and the Haunted Treehouse" premiered alongside new episodes of Season 21.