In Western tradition, an engagement ring is a ring worn by a woman indicating her engagement to be married. Conventionally, the ring is presented as a betrothal gift by a man to his prospective bride while he proposes marriage or directly after she accepts his marriage proposal. It represents a formal agreement to future marriage.
In some countries, such as the United States and United Kingdom, it is worn on the left-hand ring finger, while in other countries, such as Poland and Ukraine, it is customary for the ring to be worn on the right-hand. Similar traditions purportedly date to classical times, dating back from an early usage reportedly refferring to the fourth finger of the left hand as containing the vena amoris or "vein of love".
In the United States and Canada today it is becoming more common, but still quite rare, that a woman will also buy her partner an engagement ring (also called a promise ring or 'management' ring) at the time of the engagement.