The most useful edition of the Divine Comedy for students proposing to make a careful study of the poem is that of Scartazzini, with notes in Italian, 3 vols., and Prolegomeni, 1 vol., Leipzig, 1874-1890.
The English reader will find Mr. Longfellow's comment of great service, but it leaves many points of interest untouched.
More is required than any single comment affords, and among the books which may be commended, but which must be read with discrimination, are: A Shadow of Dante, by Miss M. F. Rossetti, London, 1871; A Companion to Dante from the German of Scartazzini, by A. J. Butler, London, 1893 (valuable, but with much questionable speculation and interpretation); Dante's Divine Comedy, its Scope and Value, by Hettinger, translated by Bowden, London, 1887 (interesting, but not always trustworthy); the essays on Dante by Lowell, Church, Caird and Carlyle, in their respective works.
The history of the text of the Divine Comedy is told by Karl Witte in the Prolegomeni to his admirable edition, Berlin, 1862, 4tc. And, in addition to this, every student of the text must have recourse to Dr. Moore's important work on The textual criticism of the Divine Comedy, Cambridge, Eng., 1889, 8vo.
The Vocabolario Dantesco, of Blanc, Leipzig, 1852, 8vo. (of which an edition in English is needed), translated into Italian by Carbone, Florence, 1859, and the Concordance of the Divina Commedia, by Professor E. A. Fay, 8vo., 1888, published by Ginn & Co., Boston, for The Dante Society, Cambridge, Mass., are indispensable to the student.