| Person | Type | Job | Role(s) |
|---|---|---|---|
 Audrey Geisel | Crew | Production | Executive Producer |
 Chris Wedge | Crew | Production | Executive Producer |
Christian Kaplan | Crew | Production | Casting Director |
 Chris Meledandri | Crew | Production | Executive Producer |
 Cinco Paul | Crew | Writing | Screenplay |
 Dennis Leonard | Crew | Sound | Supervising Sound Editor |
 Dr. Seuss | Crew | Writing | Book |
Jeannine Berger | Crew | Crew | Post Production Supervisor |
 Jimmy Hayward | Crew | Directing | Director |
 John Powell | Crew | Sound | Original Music Composer |
 Karen Disher | Crew | Art | Storyboard Artist |
 Ken Daurio | Crew | Writing | Screenplay |
 Randy Thom | Crew | Sound | Sound Designer, Supervising Sound Editor |
Ricardo Curtis | Crew | Writing | Head of Story |
 Rich Moore | Crew | Art | Additional Storyboarding |
 Steve Martino | Crew | Directing | Director |
Thomas A. Carlson | Crew | Sound | Supervising Music Editor |
Tim Nordquist | Crew | Editing | Editor |
Arun Ram-Mohan | Crew | Lighting | Lighting Artist |
Barry E. Jackson | Crew | Visual Effects | Visual Development |
Bob Gordon | Crew | Production | Producer |
Bruce Anderson | Crew | Production | Producer |
 Crystal Chesney | Crew | Art | Additional Storyboarding |
Michael Knapp | Crew | Art | Set Designer |
 J.G. Quintel | Crew | Art | Additional Storyboarding |
Nash Dunnigan | Crew | Art | Set Designer |
Jeff Siergey | Crew | Writing | Writer |
 Cal Brunker | Crew | Writing | Storyboard |
Thomas Cardone | Crew | Art | Art Direction |
Rhett Collier | Crew | Visual Effects | Senior Visual Effects Supervisor |
 Paul Downs | Crew | Visual Effects | Animation |
Alen Lai | Crew | Visual Effects | Senior Visual Effects Supervisor |
Stephanie Arnett | Crew | Art | Additional Storyboarding |
 Moroni Taylor | Crew | Art | Storyboard Artist |
Jake Parker | Crew | Art | Set Designer |
Guillermo Willie Real | Crew | Art | Set Designer |
Jamie Kirschenbaum | Crew | Visual Effects | Senior Visual Effects Supervisor |
Kyle Macnaughton | Crew | Art | Set Designer |
Lizette Vega | Crew | Art | Set Designer |
 Amy Poehler | Cast | Actress | Sally O'Malley (voice) |
 Bill Farmer | Cast | Actor | Willie Bear (voice) |
 Bob Bergen | Cast | Actor | Additional Voices (voice) |
 Carol Burnett | Cast | Actress | Kangaroo (voice) |
 Charles Osgood | Cast | Actor | Narrator (voice) |
 Colleen O'Shaughnessey | Cast | Actress | Angela (voice) |
 Dan Fogler | Cast | Actor | Councilman / Yummo Wickersham (voice) |
 Danny Mann | Cast | Actor | Additional Voices (voice) |
 Debi Derryberry | Cast | Actress | Who Mom (voice) |
 Heather Goldenhersh | Cast | Actress | Who Girl (voice) |
 Isla Fisher | Cast | Actress | Dr. Mary Lou Larue (voice) |
 Jack Angel | Cast | Actor | Old Time Who (voice) |
 Jaime Pressly | Cast | Actress | Mrs. Quilligan (voice) |
 Jess Harnell | Cast | Actor | Another Who (voice) |
 Jesse McCartney | Cast | Actor | JoJo (voice) |
 Jim Carrey | Cast | Actor | Horton (voice) |
Jimmy Hayward | Cast | Actor | Obnoxious Who (voice) |
 Joe Pasquale | Cast | Actor | The Dentist (voice) |
 John Cygan | Cast | Actor | Who (voice) |
Karen Disher | Cast | Actress | Who Kid (voice) |
 Laraine Newman | Cast | Actress | Glummox Mom (voice) |
 Marshall Efron | Cast | Actor | Wickersham Guard 1 (voice) |
 Mickie McGowan | Cast | Actress | Additional Voices (voice) |
 Mona Marshall | Cast | Actress | Additional Voices (voice) |
 Niecy Nash | Cast | Actress | Miss Yelp (voice) |
 Seth Rogen | Cast | Actor | Morton (voice) |
 Sherry Lynn | Cast | Actress | Additional Voices (voice) |
 Steve Carell | Cast | Actor | Mayor (voice) |
 Teresa Ganzel | Cast | Actress | Additional Voices (voice) |
Tim Nordquist | Cast | Wickersham Guard 2 (voice) | |
 Will Arnett | Cast | Actor | Vlad (voice) |
 Ariel Winter | Cast | Actress | Additional Voices (voice) |
Caitlin Rose Anderson | Cast | Helen (voice) | |
Connor Anderson | Cast | Who Child #1 (voice) | |
Emily Anderson | Cast | Heather (voice) | |
 Grace Rolek | Cast | Actress | Additional Voices (voice) |
Jason Fricchione | Cast | Actor | Joe (voice) |
Jeff Biancalana | Cast | Additional Voices (voice) | |
Jennessa Rose | Cast | Additional Voices (voice) | |
 Joey King | Cast | Actress | Katie (voice) |
 Jonah Hill | Cast | Actor | Tommy (voice) |
 Josh Flitter | Cast | Actor | Rudy (voice) |
Kathy Graves Toon | Cast | Additional Voice (voice) | |
 Laura Ortiz | Cast | Actress | Jessica (voice) |
 Madison Davenport | Cast | Actress | Additional Voices (voice) |
 Samantha Droke | Cast | Actress | Hildy / Holly (voice) |
 Selena Gomez | Cast | Actress | Helga (voice) |
 Isabella Acres | Cast | Actress | Additional Voices (voice) |
 Madison Pettis | Cast | Actress | Additional Voices (voice) |
Shelby Adamowsky | Cast | Actress | Hedy / Hooly (voice) |
 Jan Rabson | Cast | Actor | Town Cryer (voice) |
 Fletcher Sheridan | Cast | Actor | Jojo (singing voice) (uncredited) |
Christina Martino | Cast | Heidi / Haley (voice) | |
Ellie Martino | Cast | Hanna (voice) | |
| Person | Type | Job | Role(s) |
