In Western tradition, an engagement ring is a ring worn by a woman indicating her engagement to be married. In some countries, such as the 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. By modern convention in countries such as the United States, the ring is usually presented as a betrothal gift by a man to his prospective bride while or directly after she accepts his marriage proposal. It represents a formal agreement to future marriage.
Similar traditions purportedly date to classical times, dating back from an early usage reportedly referring 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 an engagement or promise ring for her partner at the time of the engagement.
In Egypt, Brazil and many European countries, both the man and the woman usually wear engagement rings, most often in the form of matching plain bands of white, yellow, or rose gold. In these countries the man's engagement ring often also eventually serves as the wedding ring. Some men wear two rings, but this is rarer. The woman's wedding ring can sometimes have a precious stone. In Spain, the woman sometimes buys an engagement wristwatch for the man after accepting a marriage proposal.
The price for an engagement ring can vary considerably. Usually, they can be found within the range of a few hundred dollars to several hundred thousand dollars. Price varies by the material used, the value of the gemstone, and retailer. A conventional buying price ranging from two to three months wages for a ring guideline originated from De Beers marketing materials in the early 20th century, in an effort to increase the sale of diamonds.
When shopping for rings with one or more diamonds, the price can depend significantly on the carat weight, color, clarity and cut of the diamond, otherwise known as gemological characteristics of the diamond. While less frequent, the practice of substituting other gemstones such as sapphires, rubies, moissanite, emeralds, etc occurs to honor tradition, reduce the price of the ring, or to make it more unique.
With more and more couples living together prior to marriage, however, it is becoming more common for a couple to select the engagement ring while purchasing a wedding band together. In countries where both partners wear engagement rings, the matching rings tend to be purchased together.
One case in New South Wales, Australia ended in the man suing his former fiancée because she threw the ring in the trash after telling her she could keep it despite the marriage proposal failing. The Supreme Court of New South Wales held that despite what the man said, the ring remained a conditional gift (partly because his saying that she could keep it was partly due to his desire to salvage the relationship) and she was ordered to pay him its AUD$15,250 cost.
Tradition generally holds that if the betrothal fails because the man himself breaks off the engagement, the woman is not obliged to return the ring. Legally, this condition can be subject to either a modified or a strict fault rule. Under the former, the fiancé can demand the return of the ring unless he breaks the engagement. Under the latter, the fiancé is entitled to the return unless his actions caused the breakup of the relationship, the same as the traditional approach. However, a no-fault rule is being advanced in some jurisdictions, under which the fiancé is always entitled to the return of the ring. The ring only becomes the property of the woman when marriage occurs. An unconditional gift approach is another possibility, wherein the ring is always treated as a gift, to be kept by the fiancée whether or not the relationship progresses to marriage. Recent court rulings have determined that the date in which the ring was offered can determine the condition of the gift. e.g. Valentine's Day and Christmas are nationally recognized as gift giving holidays. A ring offered in the form of a Christmas present will likely remain the personal property of the recipient in the event of a break up.
In the United Kingdom, the gift of an engagement ring is presumed to be an absolute gift to the fiancée. This presumption may be rebutted however by proving that the ring was given on condition (express or implied) that it must be returned if the marriage did not take place, for whatever reason. This was decided in the case Jacobs v Davis  2 KB 532.