High atop Mt. Crumpit lives The Grinch (JIM CARREY), a surly curmudgeon who hates Christmas and the people of Whoville who live in the valley below him and so thoroughly enjoy the season. Among them is young Cindy Lou Who (TAYLOR MOMSEN) who's seemingly the only one to question the real meaning of Christmas; her postmaster father, Lou (BILL IRWIN); and her mother, Betty (MOLLY SHANNON), who's determined to beat their neighbor, Martha May Whovier (CHRISTINE BARANSKI), in a lighting decoration contest.
Donning a disguise and infiltrating Whoville, the Grinch - who's happy that his heart is two times too small and shrinking - tries to disrupt the holiday festivities - much to the chagrin of Mayor May Who (JEFFREY TAMBOR) - but the townspeople's spirits are inextinguishable. What he does accomplish, however, is the sparking of curiosity in Cindy Lou about him. Interviewing the locals, she soon discovers the history of the Grinch and why he hates Christmas so much.
Back atop Mt. Crumpit and with only hours before Christmas, the Grinch is becoming increasingly agitated at the music and good cheer rising up from Whoville. As such, he concocts a plan to steal Christmas and thus, with the aide of his canine companion, Max, he sets out to do just that, hoping that once and for all he'll rid the town of its Christmas spirit.