Three groomsmen stand to the right of the groom and three bridesmaids stand to the left of the bride in this wedding in Kampot, Cambodia.

Best man is the chief male assistant to the bridegroom at a wedding.

In North America and Europe, the groom extends this honour to someone who is close to him, generally either a brother or his closest male friend. When the groom wishes to give this honor to a woman, she may be termed the best woman or best person, or may still be referred to as the 'best man'. The bride's equivalent of the best man is the maid or matron of honour. A gender-neutral term is honor attendant.

While the best man's required duties are only those of a friend, in the context of an American/British white wedding, the best man will typically:

• assist the groom on the wedding day,

• keep the wedding rings safe until needed during the ceremony,

• act as a legal witness to the marriage, and make a toast to the bride and groom at the reception.

• In the past, the bachelor party was typically scheduled for a convenient evening during the week before the wedding. A type of farewell dinner, it was always hosted, and therefore organized and paid for, by the bridegroom. Common slang names for this event are bachelor party, stag do or bucks' night in different parts of the world. In many areas, this dinner is now most commonly organized by the best man, and the costs are shared by all of the participants.

• The best man, or honor attendants in general, are not universal customs. Even in places where a best man is customary, the role may be quite different when compared to other areas or times.

• In most modern, English-speaking countries, the best man is simply the groom's closest male friend. Some authors believe that the best man derives from ancient customs of marriage by kidnapping, or from defending the groom from would-be kidnappers.

• At Eastern Orthodox weddings in Greece, the best man is often also the koumbaros or religious sponsor, and is traditionally the groom's godfather. The koumbaros (or koumbara, if a woman) is an honored participant who crowns the couple and participates in circling the altar three times. In some areas, this person also pays for all the wedding expenses.

• In Ukraine a best man is responsible for guarding the bride during the wedding festivities. When he or the groom steps away, the bride gets "kidnapped" or has a shoe stolen. Then the groom or the best man must pay a ransom in exchange for returning the bride, usually by paying money (which is given to the bride) or by doing something embarrassing.

• In Uganda a best man is expected to guide the newlyweds in the ways of marriage. This means that ideally a best man must be married, preferably to one wife and should be in position to give sound, tried and tested advice. A best man must be a confidant and be discreet about the details he shares with the new couple.

• In Bhutan the best man presents himself at the wedding as a ceremonial guardian to both bride and groom. Thereafter he entertains the guests, sometimes for several hours.