Season 21

The twenty-first season of the television series started airing in the UK on 18th September 2017 and 15th December 2017 for the US.

Songs

 * Set Friendship in Motion
 * Doing it Right (CGI Version)
 * Trying (CGI Version)

Characters
Oliver, Whiff, Hiro, Scruff, Connor, Timothy, Samson, Hugo, Marion, Rusty, Duncan, Toad, Bradford, Alfie, Captain, Merrick, Mr. Percival and Fergus Duncan are also likely to appear.
 * Thomas
 * Edward
 * Henry
 * Gordon
 * James
 * Percy
 * Toby
 * Donald and Douglas
 * Harvey
 * Emily
 * Spencer
 * Rosie
 * Belle
 * Stephen
 * Porter
 * Ryan
 * Glynn
 * Diesel
 * Daisy
 * Mavis
 * 'Arry and Bert
 * Salty
 * Dart
 * Den
 * Sidney
 * Paxton
 * Philip
 * Flynn
 * Skarloey
 * Victor
 * Luke
 * Millie
 * Bert
 * Rex
 * Annie and Clarabel
 * Henrietta
 * Judy and Jerome
 * Terence
 * Bertie
 * Bulgy
 * Kevin
 * Harold
 * Cranky
 * Big Mickey
 * Reg
 * Sir Topham Hatt
 * Lady Hatt
 * Stephen Hatt
 * Bridget Hatt
 * Dowager Hatt
 * Lord Callan
 * Farmer McColl
 * The Duke and Duchess of Boxford
 * The Mayor of Sodor
 * Sir Robert Norramby
 * The Grumpy Passenger
 * The Great Composer
 * The Bird Watcher
 * The Blond-haired Boy
 * Albert's Wife
 * Thomas the Baby
 * James' Driver
 * Bertie's Driver
 * Farmer Finney (not named)
 * Skiff
 * Rocky
 * Mike
 * Duck
 * Bill and Ben
 * Stanley
 * Charlie
 * Caitlin
 * Norman
 * Stafford
 * Winston
 * Rheneas
 * Sir Handel
 * Peter Sam
 * Slip Coaches
 * Trevor
 * Butch
 * Jack
 * Oliver the Excavator
 * Max and Monty
 * Owen (cameo)
 * Jem Cole
 * The Thin Clergyman (cameo)
 * The Fat Clergyman (cameo)
 * Mr. Bubbles
 * Captain Joe
 * The Teacher (cameo)
 * Sodor United Football Team (cameo)
 * The Search and Rescue Manager (cameo)
 * The Ginger-haired Boy (cameo)
 * One of Dowager Hatt's Friends (cameo)
 * The Welsh Bird Watcher (cameo)
 * The Lady with the Big Hat (cameo)
 * The Great Railway Show Judge (cameo)
 * Daisy's Fitter (mentioned)

Characters Introduced

 * Hannah
 * Carly
 * The Sea Serpents
 * The Lady in the Yellow Dress and Hat
 * The Woodsmen

UK

 * Mark Moraghan as the Narrator
 * John Hasler as Thomas
 * Keith Wickham as Edward, Henry, Gordon, Harvey, Glynn, Salty, Den, Skarloey, Bert, Bertie, Harold, The Fat Controller, Dowager Hatt, Farmer Finney, Lord Callan, the Great Composer, the Grumpy Passenger and the Woodsmen
 * Nigel Pilkington as Percy and A Passenger
 * Rob Rackstraw as James, Toby, Donald, Flynn, Big Mickey and the Red Sea Serpent
 * Joe Mills as Douglas
 * Teresa Gallagher as Emily, Belle Mavis, Annie, Clarabel, Judy, Stephen Hatt, Bridget Hatt, the Duchess of Boxford, The Blond-haired Boy, Albert's Wife and The Lady in the Yellow Dress and Hat
 * Kerry Shale as Diesel, 'Arry, the Troublesome Trucks and Kevin (Hasty Hannah only)
 * Nicola Stapleton as Rosie
 * Matt Wilkinson as Spencer, Cranky, Kevin, the Duke of Boxford, the Dock Manager and the Bird Watcher
 * William Hope as Iron Bert and Farmer McColl
 * Bob Golding as Stephen and Sidney
 * Tracy-Ann Oberman as Daisy
 * Steven Kynman as Porter, Ryan, Paxton and Dart
 * David Bedella as Victor and the Mayor of Sodor
 * Michael Legge as Luke
 * Mike Grady as Sir Robert Norramby
 * Miranda Raison as Millie
 * Tim Whitnall as Jerome and Reg
 * Maggie Ollerenshaw as Henrietta
 * Tom Stourton as Rex and Terence
 * Rasmus Hardiker as Philip and the Troublesome Trucks
 * David Menkin as Porter (Cranky at the End of the Line only)
 * Lucy Montgomery as Hannah and Carly
 * Colin McFarlane as Bulgy and Bertie's driver
 * Ian McCue as the Blue Sea Serpent
 * Christopher Ragland as the Troublesome Trucks

USA

 * Mark Moraghan as the Narrator
 * Joseph May as Thomas
 * William Hope as Edward, Toby, Iron Bert, Farmer McColl, the Duke of Boxford and the Dock Manager
 * Kerry Shale as Henry, Gordon, Diesel, the Troublesome Trucks, Harold and Kevin
 * Rob Rackstraw as James, Donald, Flynn, Big Mickey and the Red Sea Serpent
 * Christopher Ragland as Percy and the Troublesome Trucks
 * Joe Mills as Douglas
 * Jules de Jongh as Emily and the Duchess of Boxford
 * Keith Wickham as Harvey, Glynn, Salty, Den, Skarloey, Bert, Bertie, Sir Topham Hatt, Dowager Hatt, Lord Callan, Farmer Finney, the Great Composer, the Grumpy Passenger and the Woodsmen
 * Teresa Gallagher as Belle, Mavis, Annie, Clarabel, Judy, Stephen Hatt, Bridget Hatt, The Blond-haired Boy, Albert's Wife and The Lady in the Yellow Dress and Hat
 * Glenn Wrage as Spencer and Cranky
 * Nicola Stapleton as Rosie
 * Bob Golding as Stephen and Sidney
 * Tracy-Ann Oberman as Daisy
 * Steven Kynman as Ryan, Paxton and Dart
 * David Bedella as Victor and the Mayor of Sodor
 * Michael Legge as Luke
 * Mike Grady as Sir Robert Norramby
 * Miranda Raison as Millie
 * Tim Whitnall as Jerome and Reg
 * Maggie Ollerenshaw as Henrietta
 * Tom Stourton as Rex and Terence
 * David Menkin as Porter
 * Rasmus Hardiker as Philip and the Troublesome Trucks
 * Lucy Montgomery as Hannah and Carly
 * Colin McFarlane as Bulgy
 * Ian McCue as the Blue Sea Serpent
 * Nigel Pilkington as A Passenger

Trivia

 * Arc Productions had produced the first seven episodes and Terence Breaks the Ice before their bankruptcy.
 * This season contains the 500th episode of the show, which is P.A. Problems.
 * This is the third season not to have Thomas' name titled in any of the episodes, the first being the fifteenth season and the second being the twentieth season.
 * This season marks the first of many things:
 * Ian McCue's first season as creative executive, and the first season to feature him voicing a character.
 * Micaela Winter's first season as producer for the series.
 * Sukhmani Kaur's first season as assistant production manager.
 * Zahara Andrews' first season as production co-ordinator.
 * Alan Kennedy's first season as director of post-production.
 * Ryan Quaglia's first season post-production editor.
 * Gavin Ebedes' first season as supervising editor.
 * Nicola Stapleton's first season as part of the voice cast.
 * Terence, Bulgy and Farmer Finney's first appearances in full CGI.
 * Hackenbeck Tunnel's first appearance in full CGI.
 * Big Mickey gains a face for the first time in the television series.
 * The first season since he became head writer, not to have any episodes written by Andrew Brenner.
 * The first season to have episodes fully animated by Jam Filled.
 * This season also marks the last of three things:
 * Mark Moraghan's last season as narrator for the UK and US dubs.
 * The last season to utilize the original Thomas storytelling format.
 * Boris Andreev's last season as art director.
 * Alan Kennedy's last season as post-production supervisor.
 * Gavin Ebedes' last season as editor.
 * This is the no-longer shortest season to date, with there only being 18 episodes. There were 26 episodes planned, but eight were going to released on New DVD Bumps and Rides