Banking began with the first prototype banks of merchants of the ancient world, which made grain loans to farmers and traders who carried goods between cities and this system is known as a barter system.This began around 2000 BC in Assyria and Babylonia. Later, in ancient Greece and during the Roman Empire, lenders based in temples made loans and added two important innovations: they accepted deposits and changed money. Archaeology from this period in ancient China and India also shows evidence of money lending activity.

The origins of modern banking can be traced to medieval and early Renaissance Italy, to the rich cities in the centre and north like Florence, Lucca, Siena, Venice and Genoa. The Bardi and Peruzzi families dominated banking in 14th-century Florence, establishing branches in many other parts of Europe. One of the most famous Italian banks was the Medici Bank, set up by Giovanni di Bicci de' Medici in 1397. The earliest known state deposit bank, Banco di San Giorgio (Bank of St. George), was founded in 1407 at Genoa, Italy.

Modern banking practices, including fractional reserve banking and the issue of banknotes, emerged in the 17th and 18th centuries. Merchants started to store their gold with the goldsmiths of London, who possessed private vaults, and charged a fee for that service. In exchange for each deposit of precious metal, the goldsmiths issued receipts certifying the quantity and purity of the metal they held as a bailee; these receipts could not be assigned, only the original depositor could collect the stored goods.

Gradually the goldsmiths began to lend the money out on behalf of the depositor, which led to the development of modern banking practices; promissory notes (which evolved into banknotes) were issued for money deposited as a loan to the goldsmith. The goldsmith paid interest on these deposits. Since the promissory notes were payable on demand, and the advances (loans) to the goldsmith's customers were repayable over a longer time period, this was an early form of fractional reserve banking. The promissory notes developed into an assignable instrument which could circulate as a safe and convenient form of money backed by the goldsmith's promise to pay, allowing goldsmiths to advance loans with little risk of default. Thus, the goldsmiths of London became the forerunners of banking by creating new money based on credit.

The Bank of England was the first to begin the permanent issue of banknotes, in 1695. The Royal Bank of Scotland established the first overdraft facility in 1728. By the beginning of the 19th century a bankers' clearing house was established in London to allow multiple banks to clear transactions. The Rothschilds pioneered international finance on a large scale, financing the purchase of the Suez canal for the British government.

The word bank was borrowed in Middle English from Middle French banque, from Old Italian banco, meaning "table", from Old High German banc, bank "bench, counter". Benches were used as makeshift desks or exchange counters during the Renaissance by Jewish Florentine bankers, who used to make their transactions atop desks covered by green tablecloths.

The definition of a bank varies from country to country. See the relevant country pages under for more information.

Under English common law, a banker is defined as a person who carries on the business of banking, which is specified as:

• conducting current accounts for his customers,
• paying cheques drawn on him/her and
• collecting cheques for his/her customers.

In most common law jurisdictions there is a Bills of Exchange Act that codifies the law in relation to negotiable instruments, including cheques, and this Act contains a statutory definition of the term banker: banker includes a body of persons, whether incorporated or not, who carry on the business of banking' (Section 2, Interpretation). Although this definition seems circular, it is actually functional, because it ensures that the legal basis for bank transactions such as cheques does not depend on how the bank is structured or regulated.

The business of banking is in many English common law countries not defined by statute but by common law, the definition above. In other English common law jurisdictions there are statutory definitions of the business of banking or banking business. When looking at these definitions it is important to keep in mind that they are defining the business of banking for the purposes of the legislation, and not necessarily in general. In particular, most of the definitions are from legislation that has the purpose of regulating and supervising banks rather than regulating the actual business of banking. However, in many cases the statutory definition closely mirrors the common law one. Examples of statutory definitions:

• "banking business" means the business of receiving money on current or deposit account, paying and collecting cheques drawn by or paid in by customers, the making of advances to customers, and includes such other business as the Authority may prescribe for the purposes of this Act; (Banking Act (Singapore), Section 2, Interpretation).
• "banking business" means the business of either or both of the following:

Since the advent of EFTPOS (Electronic Funds Transfer at Point Of Sale), direct credit, direct debit and internet banking, the cheque has lost its primacy in most banking systems as a payment instrument. This has led legal theorists to suggest that the cheque based definition should be broadened to include financial institutions that conduct current accounts for customers and enable customers to pay and be paid by third parties, even if they do not pay and collect cheques .

Standard business

Banks act as payment agents by conducting checking or current accounts for customers, paying cheques drawn by customers in the bank, and collecting cheques deposited to customers' current accounts. Banks also enable customer payments via other payment methods such as Automated Clearing House (ACH), Wire transfers or telegraphic transfer, EFTPOS, and automated teller machines (ATMs).

Banks borrow money by accepting funds deposited on current accounts, by accepting term deposits, and by issuing debt securities such as banknotes and bonds. Banks lend money by making advances to customers on current accounts, by making installment loans, and by investing in marketable debt securities and other forms of money lending.

Banks provide different payment services, and a bank account is considered indispensable by most businesses and individuals. Non-banks that provide payment services such as remittance companies are normally not considered as an adequate substitute for a bank account.

Banks can create new money when they make a loan. New loans throughout the banking system generate new deposits elsewhere in the system. The money supply is usually increased by the act of lending, and reduced when loans are repaid faster than new ones are generated. In the United Kingdom between 1997 and 2007, there was an increase in the money supply, largely caused by much more bank lending, which served to push up property prices and increase private debt. The amount of money in the economy as measured by M4 in the UK went from £750 billion to £1700 billion between 1997 and 2007, much of the increase caused by bank lending. If all the banks increase their lending together, then they can expect new deposits to return to them and the amount of money in the economy will increase. Excessive or risky lending can cause borrowers to default, the banks then become more cautious, so there is less lending and therefore less money so that the economy can go from boom to bust as happened in the UK and many other Western economies after 2007.

Range of activities

Activities undertaken by banks include personal banking, corporate banking, investment banking, private banking, transaction banking, insurance, consumer finance, foreign exchange trading, commodity trading, trading in equities, futures and options trading and money market trading.

Channels

Banks offer many different channels to access their banking and other services:

• Branch, in-person banking in a retail location
• Automated teller machine banking adjacent to or remote from the bank
• Bank by mail: Most banks accept cheque deposits via mail and use mail to communicate to their customers
• Online banking over the Internet to perform multiple types of transactions
• Mobile banking is using one's mobile phone to conduct banking transactions
• Telephone banking allows customers to conduct transactions over the telephone with an automated attendant, or when requested, with a telephone operator
• Video banking performs banking transactions or professional banking consultations via a remote video and audio connection. Video banking can be performed via purpose built banking transaction machines (similar to an Automated teller machine) or via a video conference enabled bank branch clarification
• Relationship manager, mostly for private banking or business banking, who visits customers at their homes or businesses
• Direct Selling Agent, who works for the bank based on a contract, whose main job is to increase the customer base for the bank

Business models

A bank can generate revenue in a variety of different ways including interest, transaction fees and financial advice. Traditionally, the most significant method is via charging interest on the capital it lends out to customers.