This was the 15th appearance of the men's 100 metre freestyle. The event has been held at every Summer Olympics except 1900 (when the shortest freestyle was the 200 metres), though the 1904 version was measured in yards rather than metres. One of the eight finalists from the 1964 Games returned: silver medalist
Bobby McGregor of Great Britain. The favorite coming into the Games was
Zac Zorn, who had matched the world record at the U.S. trials. However, Zorn had struggled the week before the competition with illness. His teammates,
Ken Walsh (whose record it was that Zorn had tied) and young butterfly specialist
Mark Spitz, were strong contenders, as was McGregor (who had won the European championship). Barbados, Costa Rica, El Salvador, Ireland, Jamaica, Lebanon, and Trinidad and Tobago each made their debut in the event; West Germany competed separately for the first time. The United States made its 15th appearance, having competed at each edition of the event to date. ==Competition format==