The Wonderful Adventures of Nils is a work of fiction by the Swedish writer Selma Lagerlöf. It was originally published in two books, 1906 and 1907, and was first published in English as The Wonderful Adventures of Nils in 1907 and Further Adventures of Nils in 1911. The two parts are usually published together, in English as The Wonderful Adventures of Nils, but that name may also refer to the first part alone.

The book is about a young lad, Nils Holgersson, whose "chief delight was to eat and sleep, and after that he liked best to make mischief". He takes great delight in hurting the animals in his family farm. Nils captures a tomte in a net while his family are at church and have left him home to memorize chapters from the Bible. The tomte proposes to Nils that if Nils frees him, the tomte will give him a huge gold coin. Nils rejects the offer and the tomte turns Nils into a tomte, which leaves him shrunken and able to talk with animals, who are thrilled to see the boy reduced to their size and are angry and hungry for revenge. While this is happening, wild geese are flying over the farm on one of their migrations, and Martin, the farm's white goose attempts to join the wild ones. In an attempt to salvage something before his family returns, Nils holds on to Martin's neck as he successfully takes off and joins the wild birds.