The underlying instrument is the financial instrument upon which the structured product is based. Price movements in the underlying instrument are the key influencing factor in the current market value of a structured product. Today, underlying instruments usually take the form of shares, indices, currencies, commodities, bonds or futures. Frequently, issuers define their own underlying instruments, such as self-created indices or precisely defined share baskets. Depending on the terms and conditions of the product, the precise composition of these underlying instruments can also change during the term to maturity.