The Canon of Scripture. 
How was it put together? 

The authenticity of the Old Testament text was recognized in phases. The Pentateuch (the Law, or the first five books of the Bible) was recognized as authoritative (canonized) as Ezra read it in 444 BC (Nehemiah 8–10). Much of the prophets’ writings were accepted between 200 and 300 BC. Acceptance came, as much of what they predicted took place. The final recognition of the Old Testament text was affirmed at a synod of Jewish rabbis in Jamnia in AD 90. The authority of the Old Testament is furthered by the fact that the New Testament authoritatively quotes or alludes to it over 250 times.
The authority of all twenty-seven New Testament books was finally affirmed in AD 397 at the third Council of Carthage. Charles Ryrie states,

The Bible is self-authenticating, and the church councils have only recognized the authority already inherent in the book themselves...it is important to remember that the books of the Bible were authentic (canon) before any test of man was put to them. In the same manner, as an intelligent person is intelligent before any test of intelligence is put to him or her. The test merely confirms what is already there. The early Church used several meetings (called Councils) of learned men to verify, affirm and recognize that certain books were indeed worthy of inclusion in the Bible. They did not create the authenticity of the Bible but merely confirmed what was already present.1

The three tests placed upon the New Testament writings to determine their authenticity were the following:

1. Authorship.

Eyewitness evidence. All the writings had to be either written or backed by an apostle of Jesus Christ. Peter backed the writings of Mark and Paul backed the writings of Luke.

2. Agreement. 

Internal evidence. The content of the writings had to agree with the revealed will of God. The Old Testament was a good source of comparison for this.

3. Acceptance. 

External Evidence. All the writings had to receive unanimous acceptance by the early churches. The early Church was in surprising agreement among itself as to which writings were authentic and which were not.

Summary. 

The Bible is the most amazing body of literature in all of human history. It stands alone as a one-of-a-kind treatise. It is completely unique. Its self-agreement, prophetic fulfillment, and transforming power, put it in a category all its own. It answers the deepest questions, addresses the most pressing needs, and solves the most important problems of life. It humbles the prideful, softens the hardened, comforts the sorrowful, guides the lost, and saves those destined to perish. It provides peace in the midst of turmoil, furnishes the joy of forgiveness, and gives eager expectation (hope) for the life to come. It is Scripture. It is the Word of God.

We also thank God continually because, when you received the Word of God, which you heard from us, you accepted it not as the word of men, but as it actually is, the Word of God, which is at work in you who believe (1 Thessalonians 2:13, NIV).

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Footnote. 

1. Charles Ryrie, The Ryrie Study Bible (Chicago, IL: Moody Press, 1978), 1961.