This study represents an effort to analyze the forms used by Flor Peeters in his Thirty Chorale Preludes on Well-Known Hymn Tunes, op. 68, 69, and 70. Through this analysis it has been found that Flor Peeters has systematically used certain devices in the treatment of the cantus firmus. Furthermore, these devices can be used as a criterion in developing a classification system for the chorale preludes, which logically divide into six groups or types. The first type includes the chorale preludes in which the composition begins immediately with the first phrase of the chorale melody and continues without interruption to the end of the melody. The chorale melody is used in its entirety, the last note occasionally being sustained as an inverted organ point or organ point to form a coda. The chorale melody appears without ornamentation, but the rhythm may be subject to augmentation or diminution. The second type resembles the first type, with the exception that the chorale melody has been treated with ornamentation. Included in the third type are the chorale preludes in which the chorale melody appears in detached phrases, each phrase being separated from the next by an interlude or transition, the first phrase usually being preceded by an introduction. The chorale melody appears without ornamentation, but the rhythm may be subject to augmentation or diminution. The final note of the chorale melody may be sustained as an organ point or inverted organ point. Ornamentation constitutes the major difference between the third and fourth types. In the fourth type the chorale melody has been ornamented. The fantasia-type chorale preludes included in the fifth type make free use of the chorale melody. Entire phrases of the original chorale melody are omitted. The phrases used in the composition may appear in fragments or complete phrases with rhythmic and notational changes. The sixth type contains the chorale preludes wherein the chorale melody forms the basis of a series of variations, which constitute a partita. Each of the partitas in this type consists of an opening movement, three or five variations, and a finale. The variations are usually developed according to the specifications of types I, II, and IV. A minor consideration of this study is the harmonic devices used by Flor Peeters. Secondary chords and their sevenths, as well as parallel open fifths, are characteristic of the harmonic treatment. Like the composers of the Baroque period, Flor Peeters has composed the ornamented, figured, and the partita types of chorale preludes. In the thirty compositions considered in this study there is not an example of the canonic or the motet types. Even though Flor Peeters has not adhered to these latter types, he has made use of such devices as fugal expositions and imitation.