An offshore bank is a bank that is operated and regulated under international banking license (often called offshore license), which usually prohibits the bank from establishing any business activities in the jurisdiction of establishment. Due to less regulation and transparency, accounts with offshore banks were often used to hide undeclared income. Since the 1980s, jurisdictions that provide financial services to nonresidents on a big scale can be referred to as offshore financial centres. OFCs often also levy little or no corporation tax and/or personal income and high direct taxes such as duty, making the cost of living high.

With worldwide increasing measures on CTF (combatting the financing of terrorism) and AML (anti-money laundering) compliance, the offshore banking sector in most jurisdictions was subject to changing regulations. Since 2002 the Financial Action Task Force issues the so-called FATF blacklist of "Non-Cooperative Countries or Territories" (NCCTs), which it perceived to be non-cooperative in the global fight against money laundering and terrorist financing.

An account held in a foreign offshore bank is often described as an offshore account. Typically, an individual or company will maintain an offshore account for the financial and legal advantages it provides, including but not limited to:

• Strong privacy, including bank secrecy.
• Little or no corporate taxation via tax havens.
• Protection against local, political, or financial instability.

While the term originates from the Channel Islands being "offshore" from the United Kingdom, and while most offshore banks are located in island nations to this day, the term is used figuratively to refer to any bank used for these advantages, regardless of location. Thus, some banks in landlocked Andorra, Luxembourg, and Switzerland may be described as "offshore banks".

Offshore banking has previously been associated with the underground economy and organized crime, tax evasion and money laundering; however, legally, offshore banking does not prevent assets from being subject to personal income tax on interest. Except for certain people who meet fairly complex requirements (such as perpetual travelers), the personal income tax laws of many countries (e.g., France, and the United States) make no distinction between interest earned in local banks and that earned abroad. Persons subject to US income tax, for example, are required to declare, on penalty of perjury, any foreign bank accounts—which may or may not be numbered bank accounts—they may have. Offshore banks are now required to report income to many other tax authorities, although Switzerland and certain other jurisdictions retain bank secrecy regimes that can be more difficult to deal with. This does not make the non-declaration of the income by the taxpayer or the evasion of the tax on that income legal and many OFCs have recently been important colleagues to onshore tax authorities and law enforcement against wrongdoers. Following the 9/11 attacks, there have been many calls to increase regulation on international finance, in particular concerning offshore banks, OFCs, crypto currency and clearing houses such as Clearstream, based in Luxembourg, which are possible crossroads for major illegal money flows. Most criminality involving the banking system has happened because of the regulations and controls being circumvented.