The Canonisation Process

The Bible is our final authority. But how can we be sure that all the books that are supposed to form the Bible is in the Bible? Who decides what goes into the Bible?

Divine perspective:
The short answer is God.
God, acting through human agencies, wrote the books that made up the Bible.
All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be complete, equipped for every good work. (2 Timothy 3:16-17 ESV)
First of all, you should know this: No prophecy of Scripture comes from one's own interpretation, because no prophecy ever came by the will of man; instead, men spoke from God as they were moved by the Holy Spirit. (2 Peter 1:20-21 HCSB)

Human perspective:
The short answer is no one.
Canonization is a process. While the Bible is canonized, the history of the process of canonization is not canonized. There is no authorized record of how the books got into the Bible, just various historical records on how the Old and New Testaments were canonized.