Dorothy and the Wizard in Oz is the fourth book set in the Land of Oz written by L. Frank Baum and illustrated by John R. Neill. It was published on June 18, 1908 and reunites Dorothy with the humbug Wizard from The Wonderful Wizard of Oz.

Baum, having resigned himself to writing a series of Oz books, set up elements of this book in the prior Ozma of Oz. He was not entirely pleased with this, as the introduction to Dorothy and the Wizard of Oz opens with the protest that he knows many tales of many lands, and hoped that children would permit him to tell them those tales.

Written shortly after the 1906 San Francisco earthquake and around the time Baum moved to California, the book starts with an earthquake in California. Dorothy and others are swallowed up by cracks in the earth, and fall into an underground cavern, where begin their adventures.

Very little of the story—six of the twenty chapters—actually takes place in Oz. As in Ozma of Oz before it, and in some of the books after, Oz is not the land where the adventures take place, but the land the characters are seeking as a refuge from adventure.

In the story, set after the last book, Dorothy is joining Uncle Henry in California at Hugson's Ranch, on their way home from Australia, Dorothy having visited friends in San Francisco. She strikes up an acquaintance with Hugson's nephew and her second cousin, Zeb. Dorothy, Eureka (who is Dorothy's cat) and Zeb are riding a buggy being pulled by a cab-horse named Jim when an earthquake starts and opens a crevice beneath them that sends them hurtling into the bowels of the earth.

Dorothy, Eureka, Jim, Zeb, and the buggy alight in the land of the Mangaboos, a vegetable people who accuse them of causing the Rain of Stones (what the Mangaboos call the earthquake because they are beneath the surface of the earth, and earth instead falls on them). Zeb is surprised by this strange new land, but Dorothy surmises that they are in a fairy country because they are meeting vegetable people and Jim and Eureka are now speaking. Just as they are about to be sentenced to death by the Mangaboos, a hot air balloon falls out of the sky, and in the basket is the Wizard of Oz (whom Dorothy last met as he floated away from the Emerald City).

The Wizard brags about his showmanship and with the others' aid attempts to awe the Mangaboos into sparing their lives. After defeating their wizard Gwig by slicing him in half—and showing him, as a vegetable, completely solid inside—he is appointed by the Mangaboo prince as their temporary wizard. The Wizard, Dorothy, and Zeb temporarily escape the fate of all intruders—to be cut up and planted—when they release a Princess from the garden who assumes authority. The Prince will now lose his authority and be planted himself. The cold Princess, however, vows to have Jim and Eureka killed nonetheless, so they all plan to escape higher into the earth where the Mangaboos cannot follow them due to the stronger pull of gravity the further they rise.

Dorothy, Eureka, Zeb, Jim, and the Wizard enter a beautiful green valley and the Wizard's nine tiny piglets devour an enticing fruit which they find makes them invisible. They enter a seemingly empty cottage and are welcomed by invisible people, for they have entered the Valley of Voe, whose inhabitants use their invisibility to hide from marauding bears. The inhabitants of Voe help them escape the bears and explain what lies ahead, particularly the terrible Gargoyles (a story the Voe people tell seems to indicate that by now Baum had decided that people in a fairy land do not die; even cut into pieces, an individual is still active and aware. See The Tin Woodman of Oz for another example of this).

The companions reach the base of Pyramid Mountain and meet the Braided Man halfway up. He used to make holes, Flutters (guaranteed to make any flag flutter on a windless day), and Rustles for silk skirts. One day he stacked up many postholes he had made and fell into Pyramid Mountain and since then kept shop there, continuing to make his wares. His facial hair has gotten so long, however, that he has had to braid it to keep from tripping. Dorothy had given him a blue bow, for he had tied each braid with a different color hair bow. The only color he didn't have was blue so Dorothy gave him one. They head into the land of the Gargoyles and at first repel them successfully because the winged wooden creatures are startled by loud noises. However, they do not tire and soon imprison Dorothy and her friends. They manage to escape the Gargoyles' grasp, using their detached wings and Jim's guidance.

After a close encounter with the Dragonettes, baby dragons whose mother has tied their tails to a post until she returns from hunting, they find themselves trapped in a cave which they can not exit. Dorothy suggests that she signal Ozma to bring them to Oz by using the magic belt which she'd captured from the Nome King in Ozma of Oz. She does so at a prearranged time of day, and Dorothy, the Wizard, Zeb, Eureka, and Jim arrive within the Emerald City.

Soon after renewing his acquaintance with the Emerald City staff and making the acquaintance of Ozma, the Wizard elects to remain in Oz permanently. The others' visit is highlighted by the wooden Saw-Horse beating Jim in a race and the trial of Eureka for eating Ozma's pet piglet given to her by the Wizard; in fact, the kitten is innocent and the piglet alive and well, but the obstinate Eureka will not say so. After the piglet is restored to Ozma and Zeb and Jim decide they've had enough of fairyland, Ozma then uses the magic belt to send Dorothy and Eureka back to Kansas, and Zeb and Jim back to California.