The body of his works is considerable, the earliest known being a group of five anonymous poems included in the "Songs of Divers Noblemen and Gentlemen," appended to Newman's edition of Sir Philip Sidney's "Astrophel and Stella", which appeared in 1591. In 1595, "Poemata, a collection of Latin panegyrics, elegies and epigrams" was published, winning him a considerable reputation. This was followed, in 1601, by a songbook, "A Booke of Ayres," with words by himself and music composed by himself and Philip Rosseter. The following year he published his "Observations in the Art of English Poesie," "against the vulgar and unartificial custom of riming," in favour of rhymeless verse on the model of classical quantitative verse. Campion's theories on poetry were criticized by Samuel Daniel in "Defence of Rhyme" (1603).