The B Minor Mass is Bach's only complete setting of the Ordinary, that is the five permanent sections of the ancient Christian Mass liturgy: Kyrie, Gloria, Credo, Sanctus and Agnus Dei. As with Bach's other Mass settings, all of them limited to the Kyrie and Gloria, the majority of numners consist of 'parodies', that is, of reworkings of movements from his church cantatas. In the course of the eighteenth century, the B Minor Mass was disseminated in manuscript over an astonishingly large area, extending at least from Vienna to London and thus far exceeding that of any other of Bach's vocal works. Since its initial publication in Zurich (1833-45) it has been presented in various editions, including two for the complete edition issued by the Bach Society. The most recent critical edition appeared in 1954 in the New Bach Edition, Series II, Volume I, edited by Friedrich Smend. Smend's edition very quickly sparked a musicological controversy which, after centring almost exclusively on questions of chronology, gradually came to hinge on the work's conception. Here the crucial question was whether the B Minor Mass constituted (as Smend believed) a collection of largely independent compositions, and thus was only nominally a self-contained work. Today scholars are generally of one mind that the B Minor Mass was composed in sections between 1724 and 1749, that is, over a period spanning a quarter of a century. But they are equally agreed that Bach deliberately and intentionally combined its parts so as to form a self-contained opus. Extracts taken from the Preface, by editor Christoph Wolff