Rosh Hashanah ראש השנה

The tractate opens with the fact that there are four new years: one for kings, one for cattle, one for years, one for trees. Then comes how witnesses who had seen the young moon came to Jerusalem, how they were examined, how fires were lit on the hills so that the news should travel through the country.

Here too is the account of how Rabban Gamliel accepted witnesses and Rabbi Yehoshua held them mistaken—and Gamliel ordered him to appear with his staff and his purse on the day that by his own reckoning was Yom Kippur. He obeyed: the calendar rests not on one sage's calculation but on the court's decision. The last chapter is on the sounding of the shofar and on why "the heart must be directed upward".

Order: Moed. There is Gemara in both the Babylonian and the Jerusalem Talmud.