An option strategy that combines a bull spread and a bear spread, each with a different exercise price. This strategy produces a risk-free payoff of the difference in the two exercise prices. More specifically, it consits of one call spread and one put spread, with different exercise prices and the same expration month and underlying asset. Taking a long position in the two spreads create a long box (the investor is said to be long the box). When an investor sells both spreads, he/ she is short the box (short box).

As the options get closer to expiration dates, the box will end up worth the exercise price differntial.

The box is a riskless, and often rewardless, position.