When do we say Birkat HaMazon?

Birkat HaMazon (Grace After Meals) is recited specifically after eating bread or bread-like items (pita, rolls, etc.) in the amount of at least one 'kezayit', an olive's volume, approximately 28 grams. This is the only after-blessing that is a direct Torah obligation (from Deuteronomy 8:10). The full text is quite lengthy, four blessings plus additional paragraphs, and is recited while seated. On Shabbat, holidays, and other special occasions, additional paragraphs are inserted.