This introduction to the Old Testament gets us to the idea of Old Testament canon, which is a list of books that are accepted as inspired.
It was fairly well fixed by the time of Jesus. The last time the Hebrew canon was discussed seems to be at the Council of Jamnia in 98 A.D. Two books in particular, Song of Songs and Ecclesiastes, had apparently been considered Scripture for some time, but some features about each of these works may have troubled some rabbis. The key thing to remember is that no council of rabbis picked particular books to be part of the canon. Instead, the people over the centuries had acknowledged particular writings were divinely inspired.
In fact, each part of the Old Testament was admitted into the canon almost at once, and this Jewish Council of Jamnia merely confirmed the books that were already widely accepted as canonical. It’s striking that by the time of Jesus so many different groups of people representing different Jewish backgrounds and nationalities had such a tight agreement about the Old Testament canon. Something else they agreed on was the closure of the canon. Jews believed that prophetic inspiration ceased with Malachi.