The canon of Christian Scripture has many permutations. A majority or reformed traditions possess a narrower canon, Roman Catholicism accepts the majority of the Septuagint, the Greek Orthodox accept everything in the Septuagint with the exception of IV Maccabees, and the Ethiopic church acknowledges the broadest canon in Christianity, including such works as Jubilees, I Enoch, and the Martyrdom and Ascension of Isaiah. In some quarters, there are calls to expand the canon to include the previously excluded materials found at Nag Hammadi.
The canon of Scripture has never been a nicely resolved issue. Contemporary strains in American Protestantism, largely in re-action to decades of textual criticism, have revived the argument of a complete and self authenticating canon. Unsurprisingly, this is the canon as adopted by many of the reformers. Yet, the canon has never been a nicely resolved issue. The Greek church, as mentioned, retained the Septuagint. The Latin west eventually came to utilize 4 Esdras extensively in the liturgy (and Ambrose seems to have cited it approvingly). The canon has never been self authenticating, we can demonstrate this from examining the New Testament itself - our sacred authors had a substantially larger canon then found in many of our Bibles. Jude is a fine example. The author explicitly references the Assumption of Moses and I Enoch. Now, the Assumption of Moses is an interesting book, if only for the fact that it is largely preserved in Latin and gives us a window into what books were heavily circulated in the Latin west and may or may not have influenced the theology therein, not to mention vied for canonical status. Although, the Assumption of Moses is not the only book our New Testament authors cite as authoritative. Matthew's La regula d'oro (couldn't resist) seems to indicate the author's familiarity and approval of Tobit 4:15 and Sirach 31:15. These are a few examples. You can easily pick up any critical edition of the Greek New Testament and note the parallels.
The canon isn't quite so self authenticating. Neither is the canon a settled topic among Christians today. The Roman church still utilizes 4 Esdras in its Lenten and Funeral liturgies in the form of antiphons. Yet, after Vatican II, the normally included appendix of the Latin bible (in which was found 4 Esdras) was removed. Liturgical use is often thought of a criterion for canonicity. Here we have a book still utilized in our liturgy, yet, we're still not sure what to do with it.