Answer: Ultimately, above the human authors, the Bible was written by God. Second Timothy 3:16 tells us that the Bible was "breathed out" by God. God superintended the human authors of the Bible so that, while using their own writing styles and personalities, they still recorded exactly what God intended. The Bible was not dictated by God, but it was perfectly guided and entirely inspired by Him.

Humanly speaking, the Bible was written by approximately 40 men of diverse backgrounds over the course of 1500 years. Isaiah was a prophet, Ezra was a priest, Matthew was a tax-collector, John was a fisherman, Paul was a tentmaker, Moses was a shepherd, Luke was a physician. Despite being penned by different authors over 15 centuries, the Bible does not contradict itself and does not contain any errors. The authors all present different perspectives, but they all proclaim the same one true God, and the same one way of salvation"Jesus Christ (John 14:6; Acts 4:12). Few of the books of the Bible specifically name their author. Here are the books of the Bible along with the name of who is most assumed by biblical scholars to be the author, along with the approximate date of authorship:

Genesis, Exodus, Leviticus, Numbers, Deuteronomy = Moses - 1400 B.C.
Joshua = Joshua - 1350 B.C.
Judges, Ruth, 1 Samuel, 2 Samuel = Samuel/Nathan/Gad - 1000 - 900 B.C.
1 Kings, 2 Kings = Jeremiah - 600 B.C.
1 Chronicles, 2 Chronicles, Ezra, Nehemiah = Ezra - 450 B.C.
Esther = Mordecai - 400 B.C.
Job = Moses - 1400 B.C.
Psalms = several different authors, mostly David - 1000 - 400 B.C.
Proverbs, Ecclesiastes, Song of Solomon = Solomon - 900 B.C.
Isaiah = Isaiah - 700 B.C.
Jeremiah, Lamentations = Jeremiah - 600 B.C.
Ezekiel = Ezekiel - 550 B.C.
Daniel = Daniel - 550 B.C.
Hosea = Hosea - 750 B.C.
Joel = Joel - 850 B.C.
Amos = Amos - 750 B.C.
Obadiah = Obadiah - 600 B.C.
Jonah = Jonah - 700 B.C.
Micah = Micah - 700 B.C.
Nahum = Nahum - 650 B.C.
Habakkuk = Habakkuk - 600 B.C.
Zephaniah = Zephaniah - 650 B.C.
Haggai = Haggai - 520 B.C.
Zechariah = Zechariah - 500 B.C.
Malachi = Malachi - 430 B.C.
Matthew = Matthew - A.D. 55
Mark = John Mark - A.D. 50
Luke = Luke - A.D. 60
John = John - A.D. 90
Acts = Luke - A.D. 65
Romans, 1 Corinthians, 2 Corinthians, Galatians, Ephesians, Philippians, Colossians, 1 Thessalonians, 2 Thessalonians, 1 Timothy, 2 Timothy, Titus, Philemon = Paul - A.D. 50-70
Hebrews = unknown, mostly likely Paul, Luke, Barnabas, or Apollos - A.D. 65
James = James - A.D. 45
1 Peter, 2 Peter = Peter - A.D. 60
1 John, 2 John, 3 John = John - A.D. 90
Jude = Jude - A.D. 60
Revelation = John - A.D. 90