A code duello is a set of rules for a one-on-one combat, or duel. Codes duello regulate dueling and thus help prevent vendettas between families and other social factions. They ensure that non-violent means of reaching agreement be exhausted and that harm be reduced, both by limiting the terms of engagement and by providing medical care. Finally, they ensure that the proceedings have a number of witnesses. The witnesses assure grieving members of factions of the fairness of the duel, and help provide testimony if legal authorities become involved.