The price at which a security first trades upon the opening of an exchange on a given trading day. A security's opening price is an important marker for that day's trading activity, especially for those interested in measuring short-term results, such as day traders. Additionally, securities, which experience very large intra-day gains and losses, will have those swings measured relative to their opening price for the day.

Quite commonly, a security's opening price will not be identical to its closing price. This is due to after-hours trading and to changes in investor valuations or expectations of the security occurring outside of trading hours. Nasdaq uses an approach called the "opening cross," to decide on a price level that would serve as the best opening price, given the orders that have accumulated overnight.