WELS affirms the Protestant biblical canon consisting of 66 books: the 39 books of the Old Testament (following the Hebrew canon) and the 27 books of the New Testament. The Old Testament comprises the Pentateuch, historical books, wisdom literature, and prophetic books in the traditional Protestant arrangement.

WELS explicitly rejects the deuterocanonical books (Apocrypha)—books such as Tobit, Judith, 1 and 2 Maccabees, Wisdom of Solomon, Ecclesiasticus, Baruch, and others found in Roman Catholic and Eastern Orthodox Bibles. While these may be read for edification, they are not recognized as inspired Scripture or binding for doctrine. They are considered part of the intertestamental period but not part of the authoritative canon.

The canon is closed; no additional books are being added. The criteria for canonicity include apostolic authorship or tradition, doctrinal content consistent with apostolic teaching, and acceptance by the early church. All 66 books meet these criteria and constitute the complete and final revelation of God's Word. WELS rejects all claims to additional scriptures or revelations, whether from Mormonism, Christian Science, or other sources.