Writing to Thomas Barlow in the late seventeenth century, a young correspondent requested information ‘wherein Mr. Chillingworth's peculiar excellency above other writers consisted’. Thomas Barlow replied that this excellency stood not ‘in any extraordinary knowledge he had of Antiquity’ nor in the mere accumulation of learning but ‘did arise from, and consist in his Logick, both natural; and (by exceeding great industry) acquired’. The acumen of Chillingworth's argument, indeed, has long attracted attention. More important, the enigma of much of his character and expression has awakened a mass of commentary and exposition. In the nineteenth century, James F. Stephen, Thomas Arnold, Buckle and Lecky were concerned with him mainly as a rationalist, and the logical incompatibility of much of his thought with authoritarian Laudian churchmanship. In the present century there has been no constant course of interpretation, but a recent trend, notably in the works of D. Mathew and W. Schenk, has been to stress the affinities of Laud and Chillingworth in their appreciation of an ordered Caroline society. In this article, the intention is to attempt a precise delineation of the formation and significance of Chillingworth's thought and belief; a task in which unpublished material—both in the Lambeth Palace Library and the Bodelian Library—has been invaluable.