The thesis continues the work undertaken in recent years by (in alphabetical order) James J. Marino, Scott McMillin, Paul Menzer, Simon Palfrey, Tiffany Stern, Evelyn Tribble, and others to put to use what is now known about the purpose, distribution, and usage of early modern actors' parts. The thesis applies the new methodology of reading 'in parts', or reconstituting early modern plays 'in parts', to the body of plays written by Ben Jonson. The aim of the project is to offer a reconsideration of Jonson as a man of theatre, interested not only in the presentation of his works in print, but also in their production at the Globe and at Blackfriars. By reconstructing and examining the parts through which the actors performing in Jonson's plays accessed their characters, the thesis proposes answers to the questions: how can we read and analyse Jonson's plays differently when looking at them in terms of actors' parts; did Jonson write with parts in mind; what did Jonsonian parts have to offer actors by way of challenge and guidance; what can we learn from parts about Jonson's assumptions and demands with regard to the actors; and how did actors themselves respond to those demands. These questions are significant because they engage critically with the tradition of seeing Jonson as a playwright dismissive of actors and distrustful of the theatre; they seek to establish a perspective that allows us to assess Jonson's abilities to instruct and challenge his actors through staging documents. More generally, the research contributes to the studies of the early modern rehearsal and staging practices and invites consideration of Shakespeare's part-writing techniques in contrast with those of his major rival. With no surviving early modern parts from Jonson's plays (indeed with only a handful of surviving parts from the period), the first task is to determine the level of accuracy with which the parts can be reconstructed from Jonson's printed plays. Stephen Orgel was by no means the first critic who used the example of Sejanus to assert that Jonson habitually doctored his plays before they were published, but his view has become a critical commonplace. This thesis re-examines the case of Jonson's revisions and concludes that, far from being representative, the 1605 Sejanus quarto is an anomaly which Jonson himself needed to account for in his address to the reader. It is true that Jonson cultivated a distinct style of presentation of printed material, but the evidence that he extensively tampered with the texts themselves after they were performed is scarce (again, the revisions found in the Folio versions of Every Man in His Humour and Cynthia's Revels are addressed and found to be exceptional, rather than typical), while the evidence of his pride in the original compositions and performances is much stronger. Since such enhancements as dedicatory poems, arguments (i.e. plot summaries), character sketches, or marginalia have no bearing on the shapes of actor's parts, they do not in any way compromise the reliability of the printed texts as sources from which Jonson's parts can, argues the thesis, be reconstructed with reasonable accuracy. Jonson, himself an actor and apparently a friend and admirer of a number of great actors of his age (Edward Alleyn, Nathan Field, Richard Robinson, Salomon Pavy, Richard Burbage), knew from personal experience how much depended on actors mastering, or, in their terminology, being 'perfect' in, their parts. By granting the actor access only to select portions of the complete play-text (i.e. his own lines and cues), the part effectively regulated the performance in cases when the actor had only limited knowledge of the rest of the play. Such cases seem to have been very common: documentary evidence suggests that actors had to learn their parts on their own over the course of a few weeks, and only then attended group rehearsals, most of which were concerned with 'business', not text which had already been learned. While some might have attended a reading of the play (if one was arranged for the benefit of the sharers, for instance), or gained more information about the play from their fellow actors, the parts remained their chief means of internalising their text and acquiring a sense of the play they were in. Jonson, who was not a resident playwright with any company performing in London and thus probably did not always have easy and regular access to the actors, could sometimes have taken advantage of the actors' dependence on their parts and crafted the parts as a means of exercising control over the performances of his plays. Building on this premise, the thesis examines various features of actors' parts that would have made a difference to an actor's performance. It draws on recent advancements in the studies of textual cohesion (linguistic features such as reference, substitution, ellipsis, etc.) to point out how the high and low frequency of cohesive ties (pairs of cohesively related words or phrases) in various sections of the part would have given an actor a good idea of how prominent his part was at any given moment. It examines Jonson's use of cues and patterns of cueing: like Shakespeare, Jonson was fond of using repeated cues to open up a space for improvisation, and he seems to have been aware of the need to provide the apprentices in the company with parts cued by a limited number of actors so as to allow for easier private rehearsals with their masters. The thesis also examines the common feature of Jonson's 'split jokes' - jokes that are divided across multiple parts - and asks whether any kind of comic effect can be achieved by excluding the punch line of a joke from the part that contains its setup, and the setup from the part that delivers the punch line, offering a fresh look at the nature of early modern comedy. In structural terms, the thesis considers how a narrative constituted solely by the lines present on an actor's part can diverge from the narrative of the play as a whole and how an understanding of a play as a text composed of actors' parts, as well as of acts and scenes, can help to refine arguments about Jonson's assumptions about the strengths of the companies for which he wrote. What emerges is an image of Jonson who, far from concerned only with readership, consciously developed a brand of comedy that was uniquely suited to, perhaps even relying on, the solipsistic manner in which the actors received and learned their parts.