In the banking literature the existence of financial intermediaries is generally explained in terms of the transformation of risks, terms and lot-sizes. Yet these functions could also be performed by system of perfect and complete markets. Therefore, the approach taken in Why Banks? is to start by investigating the conditions that, in the real world, render markets imperfect and incomplete, namely asymmetric information distribution and uncertainty. Incentive compatible financing instruments (standard debt contracts as well as equity participation) provide a means of solving these problems. Financial intermediaries ultimately owe their existence to their ability to save transaction costs using these instruments and to solve problems relating to the enforcement of contracts.