Birkat Hamazon ברכת המזון

All blessings before food were instituted by the sages; the one after a meal with bread—by the Torah itself. The Talmud takes it apart: the first blessing, on food for all that lives, was said by Moses when the manna fell; the second, on the land, by Joshua when they entered it; the third, on Jerusalem, by David and Solomon; the fourth was added at Yavneh.

So the table prayer turned out to be a short history of the people: wilderness, Land, Jerusalem, consolation after destruction. It is said seated, over the table at which one ate; with three present, one invites the others—the zimmun. The laws are in the seventh chapter of Berakhot.