The object of investigation in this paper is the group of Old Testament plays from the Corpus Christi cycles. The plays of Chester, York, Wakefield and the Ludus Coventriae are discussed in their cyclical sequence. The main point of each individual analysis is to define the relationship between the theological significance of the scriptural material (as it was understood in the Middle Ages) and the dramatization based on the same material. The group of plays is divided into two parts: plays on the events connected with the creation and before man's fall into sin and those on events that follow the original sin. It is shown how in the first group the theological prerequisites are presented for relationship between God and man. Where this presentation develops into dramatic action, as. in the scene of Lucifer's fall, its character becomes homiletic, demonstrating good and bad examples. The second group contains plays on significant interactions between God and man in a world tainted by sin; in these plays the shift of emphasis from theology to homiletic instruction appears regularly. Analysis shows that it keeps the plays in correspondence with the traditional liturgical function of the Old Testament readings in the Middle Ages. It appears that the roots of dramatic innovations, such as Noah's wife, are to be found in the same change of emphasis. The general theme of the Old Testament plays is closely related to the liturgical and homiletic tradition of the season of Lent and, furthermore, it is generally kept in a negative tone. For these reasons it is termed "the history of sin."