In finance, derivatives are instruments whose value changes on the basis of a single or multiple underlying asset(s), rather than on the basis of itself. It is derived from another asset that changes as well. A contract between its buyer and seller states that as the underlying asset changes, the derivative will change along with it. As a result, the actual value of any derivative comes from the change in something else. The underlying assets on which a derivative might be dependent can include stocks, bonds, a market index, commodities, or even something as simple as a weather forecast. That said, the main purpose of a derivative is so that investors can predict against one another - an investor who thinks stocks may decrease soon can set up a derivative whose price will increase for himself if the stocks change according to his prediction. In many cases, a derivative might be leveraged somehow to allow for small changes in the underlying asset to cause much larger changes in the price of the derivative.