Talmud Bavli, Rosh Hashana, 16
Rabbi Krospedai said in the name of Rabbi Yochanan: Three books are opened on Rosh Hashana: The first is for the completely righteous, the second for the completely wicked, and the third for those in the middle. The completely righteous are immediately recorded and sealed in the Book of Life. The completely wicked are immediately recorded and sentenced to the Book of Death. The fate of those who fall somewhere in the middle is suspended from Rosh Hashana until Yom Kippur. If they are acquitted – they are sealed in the Book of Life. If they are convicted, they are sentenced to the Book of Death.
According to tradition, Man was created on Rosh Hashana. The Midrash states: When HaShem created Man, He showed Man all the trees in the Garden of Eden, and said to him, "Behold, my creations are beautiful and fine. Take heed not to spoil and destroy my world, for if you do, no one will amend your deeds for you.”