The study of medieval drama is relatively new but rapidly developing area of humanistic concern. Unfortunately, however, students of the medieval drama lack accurate modern texts of the plays, all of which are now being re-edited, and complete and accurate transcriptions of the historical documents which are so important to our understanding of the history, development, and production techniques of the medieval cycle plays. Of particular importance to the history of the plays are the dramatic documents of Chester, not only because they are more numerous than those of most other cities, but also because they include the earliest and fullest descriptions of the performance of the plays. Many of these documents remain unpublished and some of the published ones contain inaccuracies; for example, of the twelve extant disbursement accounts for performances of the plays, only seven have been published and of these seven, only three are accurate. Because complete transcriptions of contemporary documents referring to the plays have been unavailable, much of the critical commentary has been speculative. While making available the extant documents, a task I am currently engaged in, will not solve all the problems of the plays, it will narrow the limits of our speculations about them and give us a firmer basis of fact upon which to work. The discussion which follows is restricted to that of the frequency of performance of the Chester plays; it is designed to report facts and correct errors about the years in which the plays were performed and to speculate about the frequency of performances for years in which the facts are few or non-existent. In addition, the paper presents a preliminary report on the Chester dramatic documents and a discussion of the kind of evidence to be found in municipal records.