http://en.wikipedia.org/wiki/Islamic_banking
"History of Islamic banking
Introduction
An early market economy and an early form of mercantilism, called "Islamic capitalism", were developed between the eighth and twelfth centuries.[4] The monetary economy of the period was based on the widely circulated currency the gold dinar, and it tied together regions that were previously economically independent.
A number of economic concepts and techniques were applied in early Islamic banking, including bills of exchange, partnership (mufawada, including limited partnerships, or mudaraba), and forms of capital (al-mal), capital accumulation (nama al-mal),[5] cheques, promissory notes,[6] trusts (see Waqf),[7] transactional accounts, loaning, ledgers and assignments.[8] Organizational enterprises independent from the state also existed in the medieval Islamic world, while the agency institution was also introduced during that time.[9][10] Many of these early capitalist concepts were adopted and further advanced in medieval Europe from the 13th century onwards.[5]
Riba
The word "riba" means interest, usury, excess, increase or addition, which according to Shariah terminology, implies any excess compensation without due consideration (consideration does not include time value of money). The definition of riba in classical Islamic jurisprudence was "surplus value without counterpart", or "to ensure equivalency in real value", and that "numerical value was immaterial."
Applying interest was acceptable under some circumstances. Currencies that were based on guarantees by a government to honor the stated value (i.e. fiat currency) or based on other materials such as paper or base metals were allowed to have interest applied to them.[11] When base metal currencies were first introduced in the Islamic world, the question of "paying a debt in a higher number of units of this fiat money being riba" was not relevant as the jurists only needed to be concerned with the real value of money (determined by weight only) rather than the numerical value. For example, it was acceptable for a loan of 1000 gold dinars to be paid back as 1050 dinars of equal aggregate weight (i.e., the value in terms of weight had to be same because all makes of coins did not carry exactly similar weight).
The biggest problem with Islamic banking is that a house loan that is Shariah compliant will cost you about 2% more than a conventional bank loan.