This study catalogues and illustrates all of the artist's books that Allan Kaprow published to accompany his happenings, from his first artist's book in 1962 to his final anthology projects of the 1990s: a total of 35 books published over 40 years. Although Kaprow was the acknowledged pioneer of the happening from the 1950s on, he is less often recognized as a pioneer in the genre of artist's books. Nonetheless, from the start Kaprow produced what he described as "activity booklets" - publications intended to function as tools to help people understand and experience such performances. He likened these booklets to "musical scores": vehicles of opportunity rather than documents of past events. But the graphic layout of his books, the originality of their structure, the literary character of their texts and their aesthetic quality as objects elevates them from ostensibly practical scores to primary examples of first-generation book art.