I found this reposting of Met. Isaiah of Denver (GOARCH) on the blog modeoflife to be quite good. If you're unclear about what the Orthodox Church uses and why, this is the post for you.
The Epistles (or, again, their pericopes) are bound together in another book, called the Apostolos, which is normally found at the chanter’s stand. Usually located next to the Apostolos on the chanter’s shelf are the twelve volumes of the Menaion, as well as the books called the Triodion and Pentekostarion, containing various segments of the Old and the New Testaments.
The fact that there is no ‘Bible’ in the church should not surprise us, since our liturgical tradition is a continuation of the practices of the early Church, when the Gospels and the letters from the Apostles (the Epistles) had been freshly written and copied for distribution to the Christian communities. The ‘Hebrew Scriptures’ (what we now call the ‘Old Testament’, comprising the Law (the first five books) and the Prophets, were likewise written on various scrolls, just as they were found in the Jewish synagogues...
Complete post here.