Haiku, for all its simplicity, grew out of a complex tradition of Japanese collaborative poetry called renga. In renga, Carter explains, a group of poets -- sometimes more than a dozen -- gather under the supervision of a renga master, or sōshō. Each poet contributes a stanza in turn, with the sōshō guiding composition by mandating the use of particular words or the exploration of certain topics. In one renga session, the poets might produce as many as 100 linked stanzas, which mutate over time to take the renga through different movements. The first verse of the renga, called a hokku, is identical to a modern haiku.