The book contains a study and critical implicit or incipit-explicit edition of an eleventh-century canon law collection based on two important major canonical collections of the eleventh century: the Collection in Five Books compiled in southern Italy, and the famous Decretum of Burchard of Worms that was quickly copied in both southern and central Italy in the eleventh century. The Collectio Toletana is one of at least twenty-five derivative collections based on the Collection in Five Books, and its length and diversity of canons make it an appropriate subject of a study and critical edition. Given the critical need for modern editions of the major early canon law collections, scholars have long been urged to channel their energies toward these and not minor and derivative collections found in one or a few codices. The complexities of producing such editions, which have becoming increasingly apparent over the past few decades, would appear to suggest more modest, circumscribed goals. However, a partial edition of a text such as produced here can be justified on several grounds even though there is no evidence as of yet that the Collectio Toletana had any influence on other collections. First, it is now clear that the Collection in Five Books was the most significant indigenous Italian collection of the first half of the eleventh century and continued to exercise great influence in canonistic studies well into the twelfth century, especially in its derivatives, of which the Collectio Toletana is one. Second, an edition of its derivatives will be useful in controlling the edition of the Collection in Five Books. Third, the light shed by the derivative collections should allow for a more finely tuned reconstruction of the original. And finally, editions and studies of the derivatives in all their peculiarity and idiosyncracy, will undoubtedly point to the existence and types of manuscripts of the Collection that were available in the eleventh century.