The Wonderful Adventures of Nils (orig. Nils Holgerssons underbara resa genom Sverige; literally Nils Holgersson's wonderful journey across Sweden) is a work of fiction by the Swedish writer Selma Lagerl f, the first women to receive Nobel Prize in literature to make the study Sweden geography fun for children. 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.

Selma Lagerl f, like many leading Swedish intellectuals of her time, was an advocate of Swedish spelling reform. When published in 1906, this book was one of the first to adopt the new spelling mandated by a government resolution on April 7, 1906 (see Svenska Akademiens Ordlista).