Football has been included in every Summer Olympics except 1896 and 1932 as a men’s competition sport while women’s football was added to the official programme in 1996.
However, according to Wikipedia an unofficial football tournament was organized during the first competition, in which an Athens XI lost to a team representing Smyrna (Izmir), then part of the Ottoman Empire. However, it is in fact unclear whether any competition took place at all; the Olympic historian Bill Mallon has written: “Supposedly a match between a Greek club and a Danish club took place. No such 1896 source supports this and we think this is an error which has been perpetuated in multiple texts. No such match occurred”.
Tournaments were played at the 1900 and 1904 games and the Intercalated Games of 1906, but these were contested by various clubs and scratch teams. Although the IOC considers the 1900 and 1904 tournaments to be official Olympic events, they are not recognized by FIFA; neither recognizes the Intercalated Games today.
In 1906 teams from Great Britain, Germany, Austria, the Netherlands and France withdrew from an unofficial competition and left Denmark, Smyrna (one Armenian, two Frenchmen and eight Britons), Athens and Thessaloniki Music Club to compete. Denmark won the final against Athens 9–0.