This is the second book of the Mishneh Torah of the Rambam, Rabbi Moshe ben Maimon. Laws of Blessings.
This chapter explains who is obligated to recite the blessing over meals, biblically or rabbinically. It covers the blessing of three who ate together, and what Zimun is. It addresses the obligation of those who eat at a wedding and the food prepared after the wedding for the first twelve months. Everyone is obligated to recite Zimun, and who is included. It also covers seven who ate bread and three who ate vegetables if they join together, and two who finished eating and a third who came if they join together. It explains how to separate groups of people who eat alone, including two groups eating in the same house, three who ate together and one went to the market or went ahead and recited the blessing, two who ate together if one can fulfill the obligation for the other, and a son for his father, a wife for her husband. Finally, it covers someone who enters a room and finds people reciting the blessing.