This thesis assesses the role of the grotesque in some of Milton's prose works from 1641 to 1651. The Renaissance grotesque has its origins in the rediscovered human-animal-plant chimeras of Roman ornamental painting, widely emulated in the Renaissance arts, and expanded to incorporate ideas of disguise, dance, attire, peculiarities of the natural world, perplexing constructs of thoughts, and motifs of metamorphosis and dream. The grotesque is one of the major intellectual and cultural developments of the Renaissance, and the thesis traces Milton's growing awareness of its literary and polemical possibilities. The first chapter begins by outlining the history of the grotesque and of theorising about it, emphasising its meaning and role in Milton's age. A new theory of the grotesque is advanced, which sees the concept as a `structure' comprising a major element - the principle - and a minor element - the agent. A seminal example of such a grotesque structure is Raphael's Vatican Loggia, in which the paintings of biblical history form the principle and the pagan chimerical ornaments the agent. Within such a structure, the agent is aesthetically dependent on the principle, yet challenges it. The remainder of the chapter examines the Renaissance aesthetic debate on the grotesque, and Milton's use of the word grotesque in Paradise Lost. The second chapter analyses Milton's polemical use of the grotesque in two anti-episcopal pamphlets, Of Reformation (1641) and Animadversions (1641). Its use in the first is seen as part of the Puritan adoption of Reformation-inspired anti-Catholic polemics, whereas the second develops a new grotesque style. As part of this, Milton joins the polemically effective grotesque potential of the Marprelate pamphlets to the more established Reformation-style grotesque. The third chapter assesses Milton's use of the grotesque in The Doctrine and Discipline of Divorce (1643). Here Milton develops the notion of grotesque love which marked by human fallibility and thus legitimises divorce. Milton also uses the grotesque to acknowledge the limitations of his authorial persona, and to hint at the equality of gender relationships within ideal marriages. The fourth chapter focuses on Areopagitica (1644) and the notion of grotesque truth developed there. Milton uses this concept to complicate his authorial persona and his attitude to the contemporary debate on licensing. In part, it is Milton's aim to increase the awareness of the implications of licensing by indirect means, through the structures of the grotesque. The fifth chapter analyses A Defence of the People of England (1651) and its polemic use of the grotesque to colour his readers' perceptions of his opponents, but also eventually to alienate himself from his European readership in an attempt to refashion his readers' conceptions of the stereotypical Puritan. The process of presenting credible arguments through an increasingly alien persona paradoxically allows Milton to make the tract's arguments appear more independent and reliable: the authority of the argument, established initially through a trustworthy spokesman, remains credible even when it is reiterated by an increasingly alienated and Puritan authorial persona. The thesis ultimately shows that Milton's use of the grotesque in prose works from 1641 to 1651 indicates a growing awareness of its complex possibilities and an increasingly daring and original use of them.