Hail and Farewell is a military event in which standing members of a division gather to welcome new members and bid goodbye to outgoing ones. The specifics of the event vary depending on what country and military branch is celebrating, In the United States, Hail and Farewell is celebrated when a new commanding officer joins a unit; it usually includes a formal or semi-formal dinner and an official welcoming ceremony.
Each unit has different traditions for conducting Hail and Farewell events. In the Navy, dinners must be black-tie events, but in other branches, semi-formal events are allowed. In addition, each unit may decide whether to make the dinner a "dine in" or "dine out" event. Dine in events may be attended only by members of the unit, while dine out events permit unit members to bring spouses or dates. In the modern military, dining out events are increasingly common.
The name Hail and Farewell comes from a poem by the Roman writer Catallus. The untitled poem, which was written before 57 BC, is known as "Catullus 101." The text was written to commemorate the death of Catallus' older brother. It concludes with the line "ave atque vale," which can be translated as "hail and farewell."