Andrew Marvell's famous polemical pamphlets against Samuel Parker, the two parts of The rehearsal transpros'd, are packed with references and allusions to other books, some very esoteric. We think we have discovered where Marvell did his reading – in the library of Arthur Annesley, first earl of Anglesey, who also protected Marvell and his bookseller from the licenser and the Stationers' Company. In this, he collaborated with the earl of Shaftesbury, the then Lord Chancellor. The implications of these discoveries go well beyond even the new bibliography, suggesting that Marvell wrote his responses to Parker under the patronage of Anglesey, and that his connections with Shaftesbury began earlier than supposed; but they also show us how one efficient and intelligent reader responded to the task of detailed controversy, by doing focused and rapid research. Would that our own had equally witty results!