The Bible is composed of 66 books written by multiple human authors over the course of 1,500 years. It is the inspired and inerrant Word of God and tells one unified story: God’s redemption of His people through Jesus Christ. The current order of Scripture is established by historical precedence. The Old Testament follows the traditional order found in the Septuagint, the Greek translation of the Hebrew Bible used by Jesus and His contemporaries. The Synoptic Gospels of the New Testament were ordered under the oversight of Augustine. The Pauline epistles (or letters) were placed according to length. Of note, all of the books were written by confirmed Jewish authors except for Luke-Acts, which were written by the Gentile Luke, and the Letter to the Hebrews, author unknown.
For reference, below is a brief overview of Holy Scripture in the order the books appear according to Reformed Tradition. A companion PDF is also available.