Somtyme, to shewe his lightnesse and maistrye,
He pleyeth Herodes upon a scaffold hye. (MilT I.3383-84)
The English mystery plays -- cyclic collections of short plays on incidents in biblical history from the Creation to the Last Judgement -- were truly popular dramas. They were intended for the people, not the court; they were patronized by the craft guilds that sponsored the individual plays (the word "mystery" refers to the crafts and trades rather than to something "inexplicable or secret"); and though there may have been occasional semi-professional actors, the roles were filled mainly by amateurs, like Absolon in the Miller's Tale, as described in the lines quoted above. These plays, in short, were civic undertakings, expressive of civic attitudes and values as well as the religious ideas that are their main concern. It is not therefore surprising that the mystery plays often offer, as a kind of aside, social comment. The authors of the mystery plays are unknown. Most of them are written in stanzas reminiscent of the popular romances, but what one should make of that is not altogether clear. The one author whose work stands out from that of the others is the so-called "Wakefield Master" (whose works are included in the Townley Cycle). Today his "Second Shepherds' Play" is by far the best known (and the most often performed) of the mystery plays. The plays survive in "cycles," of which the York and Townley cycles are the most important. The cycles are collections of individual plays, beginning with a play on the Creation and ending with a "Last Judgement." Within these limits, considerable variation is possible, but all the cycles follow the history of salvation in a series of plays depicting events in the Old and New Testaments (with much non-biblical detail).
These plays are available in slightly regularized form, with glosses for beginning readers:
The Townley and York cycles are available (without glosses) online here.
See especially The Second Shepherds' Play, Play XIII in the Townley cycle.
See also the edition of Martin Stevens and A.C. Cawley, The Towneley Plays. EETS, SS 13-14. London, 1994 [Widener 11474.5 vol. 123-14], which has very good notes and a glossary.
The mystery plays were not the only form of early popular drama. A still useful and convenient guide to the varieties is vol. I of John Matthews Manly, Specimens of Pre-Shakespearean Drama. Boston, 1900 [Widener 14414.31].
For a general survey see Stanley J. Kahrl, Traditions of Medieval English Drama. Pittsburg, 1975 [PR641.K33 1975], and for a classic study of the literary characteristics of the cycles, see V.A. Kolve, A Play Called Corpus Christi. Stanford, 1966 [PR643.C7 K6 1971].
For a bibliography of critical and scholarly work on the English drama of the time see section seven of the Bibliography.