Derivatives are financial instruments whose value is derived from an underlying asset such as a stock, commodity, currency, or index. There are two main types of derivatives - over-the-counter (OTC) derivatives which are privately negotiated contracts between two parties, and exchange-traded derivatives which are standardized contracts traded on a public exchange. Derivatives allow parties to transfer risk from one to another and are used for hedging, speculation, and arbitrage. Common derivatives include forwards, futures, and options.