Spirou & Fantasio (French: Spirou et Fantasio), commonly shortened to Spirou, is one of the most popular classic Franco-Belgian comics. The series, which has been running since 1938, shares many characteristics with other European humorous adventure comics like The Adventures of Tintin, Lucky Luke, and Asterix. It has been written and drawn by a succession of artists.

Spirou and Fantasio are the series' main characters, two adventurous journalists who run into fantastic adventures, aided by Spirou's pet squirrel Spip and their inventor friend, the Count of Champignac.

The comic strip was originally created by Rob-Vel for the launch of Le Journal de Spirou (Spirou magazine) on April 21, 1938, and published by Éditions Dupuis. The main character was originally an elevator (lift) operator (in French: un groom) for the Moustique Hotel (in reference to the publisher's chief magazine, Le Moustique), and remained dressed in his red bellhop uniform for a long time after the occupation was dropped. Spirou (the name means 'squirrel' (lit.) and 'mischievous' (fig.) in Walloon) has a pet squirrel called Spip, the series' first supporting character, who was introduced on June 8, 1939, in the story arc titled L'Héritage de Bill Money and liberated in the following week's issue, remaining a presence in all Spirou stories since.

Adding to the difficulties of magazine publication that came with the outbreak of World War II, Velter joined the army effort, and his wife Blanche Dumoulin, using the pen name Davine, continued the work on the Spirou strip, with the aid of the young Belgian artist Luc Lafnet. Spirou became the property of the publisher Dupuis (atypical in France and Belgium where most comic characters are owned by their creator(s)), who bought the character from Rob-Vel in 1943, and since then the series has belonged to no specific author. The title has therefore subsequently been passed on to several different artists and writers.

The first success came in 1943 when Joseph Gillain, known by the pen name Jijé, was given charge of the character. In 1944 Jijé introduced a new character, Fantasio, who would become Spirou's best friend and co-adventurer. Holding many artistic commitments at Spirou magazine, Jijé sought to delegate much of his work, and in 1946 he handed the series to his understudy, the young André Franquin, in the middle of the production of the story Spirou et la maison préfabriquée.

Franquin developed the strip from single gags and short serials into long adventures with complex plots and is usually considered the definitive author of the strip. He introduced a large gallery of recurring characters, notably the Count de Champignac, an elderly scientist and inventor; the buffoonish mad scientist Zorglub; Fantasio's cousin and aspiring dictator Zantafio; and the journalist Seccotine, a rare instance of a major female character in Franco-Belgian comics of this period.

One Franquin creation that went on to develop a life of its own was the Marsupilami, a fictional monkey-like creature with a tremendously long prehensile tail. The Marsupilami appears in the majority of the Franquin stories, starting in 1952 with Spirou et les héritiers. In the series, it is adopted by the duo and follows them everywhere they go. Marsupilamis in the wild take centre stage briefly in Le nid des Marsupilamis (1957) which presents Seccotine's documentary featuring a family in their natural habitat, the jungles of the fictitious South American state Palombia.

Starting with Le prisonnier du Bouddha (1959), Franquin began to work with Greg (writing) and Jidéhem (backgrounds). As in some of his later series (Bruno Brazil, Bernard Prince), Greg staged his stories in a realistic geopolitical context. Le prisonnier du Bouddha is set in mainland China, with veiled references made to the Cold War. As for QRN sur Bretzelburg, it takes place in two imaginary European countries which bring to mind pre-reunification Germany. Lastly, it is with Greg that Franquin created the famed villain Zorglub in the diptych of Z comme Zorglub and L'ombre du Z.