A financial derivative is an instrument based on or ‘derived’ from underlying assets such as shares, bonds, commodities or currencies. In general, it is an obligation to buy or sell the underlying asset at an agreed price and time in the future. Since it takes only a small down payment (margin) to purchase such an obligation, any movement in the value of the underlying asset above or below the agreed price can produce immense profits or losses relative to the original down payment. The number of instruments invented in the past few years which fit this definition is vast, and their use has become so pervasive that some professionals no longer regard the simplest derivatives, such as futures and options. It was Aristotle who first recorded a suspicion that all might not be well where derivatives were concerned. Around 330 BC, in the first book of his Politics, he wrote down the first detailed description ever recorded of an options contract in a story about the philosopher Thales of Miletus. Aristotle claims that Thales invented options.