Derivatives do not have value on their own — they derive their value from something else (the underlying asset). A stock option derives value from the stock price. An oil future derives value from oil prices. A currency forward derives value from exchange rates. They are financial instruments built on top of other financial instruments.
Four main types: futures (standardized, exchange-traded), forwards (customized, OTC), options (right but not obligation), and swaps (exchange cash flows). The global derivatives market is staggering — over $600 trillion in notional value, making it the largest financial market by far.
Warren Buffett once called derivatives "financial weapons of mass destruction" — and the 2008 crisis proved him right. Credit default swaps (a type of derivative) amplified the subprime mortgage crisis into a global financial meltdown. Despite the risks, derivatives serve vital purposes: hedging risk, price discovery, and market efficiency. Used wisely, they are essential; used recklessly, they are catastrophic.