It is the second adaptation of the book, the first one being the 1972 animated musical television special. It builds on the book by expanding the story of Ted, the previously unnamed boy who visits the Once-ler. The cast includes Zac Efron as Ted, Danny DeVito as the Lorax, and Ed Helms as the Once-ler. New characters introduced in the film are Audrey, who is voiced by Taylor Swift, Aloysius O'Hare, voiced by Rob Riggle, and Grammy Norma, voiced by Betty White. The film was a box office success although it received mixed reviews.

Plot
Theodore "Ted" Wiggins is an idealistic 12-year-old boy, who lives in "Thneedville", a walled city that, aside from its citizens, is completely artificial—everything there is made of plastic, metal, or synthetics. Ted sets out to find a real tree in order to impress Audrey, who Ted has a crush on. His energetic grandmother suggests he speak with the Once-ler about this. According to the tale Ted's grandmother mentions, the Once-ler will tell anyone about trees if brought fifteen cents, a nail, and a shell of great-great-great grandfather snail. When Ted sets off outside of Thneedville in search of the Once-ler with these items, he discovers that the outside world is a contaminated, empty, wasteland. The Once-ler agrees to tell Ted about the trees if he listens to the story over multiple visits. Ted agrees, even after the mayor of Thneedville, Aloysius O'Hare, who is also the greedy proprietor of a bottled oxygen company, confronts the boy and pressures him to stay in town. Over the course of the film, Ted continues to sneak out of O'Hare's sight with the encouragement of his grandmother and learns more of the history of the trees.

Over Ted's various visits, the Once-ler recounts the story of how he departed his family to make his fortune. After stumbling upon a lush Truffula Tree forest, Once-ler meets the guardian of the forest, the Lorax, after cutting down a Truffula Tree. The Lorax urges Once-ler to leave the forest, but Once-ler refuses. Eventually, the Once-ler promises not to chop another tree down, and the two seem to begin a friendship of sorts. Then, the young businessman's Thneed invention becomes a major success and Once-ler's family arrives to participate in the business. At first keeping his promise, the Once-ler continues Thneed production by harvesting the Truffula Tree tufts in a sustainable manner. However, soon his greedy and lazy relatives convince him to resume chopping down the trees, due to how long harvesting the tufts takes. Over time, the Once-ler's deforestation spirals into a mass overproduction. Flush with wealth, the Once-ler rationalises his short-sighted needs into arrogant self-righteousness, and the Lorax's helpless protests do not stop him. The Once-ler pollutes the sky, river and landscape, until the last Truffula Tree falls. Finally, the Once-ler is distraught, with the region uninhabitable because of his business's pollution. He is left ruined and abandoned by his own family and becomes a recluse. The Lorax sends the animals away to search for a better place to live before departing himself into the sky, leaving only a stonecut word: "Unless".

At the end of the story, the Once-ler understands the meaning behind the Lorax's last message, and gives Ted the last Truffula seed in hopes that he can plant it and make others care about real trees once more. Ted's desire to impress Audrey is now a personal mission to remind his town of the importance of nature. O'Hare, determined not to have trees undercut his business, takes heavy-handed steps such as covering Audrey's nature paintings, closing off the door that Ted uses to see the Once-ler, and forcibly searching Ted's room for the seed. Ted enlists his family and Audrey to help plant the seed, which has begun to germinate after coming into contact with water. O'Hare and his employees pursue the dissidents until they manage to elude him and reach the town center. Unfortunately, their attempt to plant the seed is interrupted by O'Hare, who rallies the population to stop them. To convince them otherwise, Ted takes an earthmover and rams down a section of the city wall to reveal the environmental destruction outside. Horrified at the sight and inspired by Ted's conviction, the crowd defies O'Hare, with his own henchmen expelling him from the town. The seed is finally planted, and Audrey kisses Ted on the cheek. Time passes and the land starts to recover; the trees grow, the animals return, and the redeemed Once-ler is happily reunited with the Lorax.

Critical response
The film received mixed reviews from critics, with criticism directed towards the film and its marketing as betraying the original message of the book. The film earned a "rotten" rating of 55% on Rotten Tomatoes based on 146 reviews and an average rating of 5.9/10, with the critical consensus saying, "Dr. Seuss' The Lorax is cute and funny enough, but the moral simplicity of the book gets lost with the zany Hollywood production values." It also has a score of 46 on Metacritic based on 30 reviews, indicating "mixed or average reviews".

New York magazine film critic David Edelstein on NPR's All Things Considered strongly objected to the movie, arguing that the Hollywood animation and writing formulas washed out the spirit of the book. "This kind of studio 3-D feature animation is all wrong for the material," he wrote. Demonstrating the poor way the book's text was used in the movie—how modern cultural styles were pasted over the text—in this excerpt from the review, Edelstein shows Audrey describing the truffula trees to Ted:
"the touch of their tufts was much softer than silk and they had the sweet smell of fresh butterfly milk" -- and  Ted says, "Wow, what does that even mean?" and Audrey says, "I know, right?" So one of the only lines that is from the book, that does have Dr. Seuss' sublime whimsy, is basically made fun of, or at least, dragged down to Earth."

Some conservatives have criticized the film for having a strong environmentalist message. Lou Dobbs, the host of Lou Dobbs Tonight on the Fox Business Network, has criticized the film as being "insidious nonsense from Hollywood," and accused "Hollywood of trying to indoctrinate children."

The film also garnered some positive reviews, from critics such as Richard Roeper who called it a "solid piece of family entertainment". Roger Moore of the Pittsburgh Tribune called the film "a feast of bright, Seuss colors and wonderful Seuss design", and supported its environmentalist message.

Box office
The film has grossed $214,030,500 in North America, and $132,273,439 in other countries, for a worldwide total of $346,303,939.

The film topped the North American box office with $17.5 million on its opening day (Friday, March 2, 2012). During the weekend, it grossed $70.2 million, easily beating the other new nationwide release, Project X ($21 million), and all other films. This was the biggest opening for an Illumination Entertainment film, and for a feature film adaptation of a book by Dr. Seuss, as well as the second largest for an environmentalist film. It also scored the third-best debut for a film opening in March, and the eighth-best of all time for an animated film. The Lorax stayed at #1 the following weekend, dropping 45% to $38.8 million and beating all new nationwide releases, including Disney's John Carter (second place). On April 11, 2012, it became the first animated film in nearly a year to gross more than $200 million in North America, since Disney's Tangled.