A custodian bank, or simply custodian, is a specialized financial institution responsible for safeguarding a firm's or individual's financial assets and is not necessarily engaged in "traditional" commercial or consumer/retail banking such as mortgage or personal lending, branch banking, personal accounts, ATMs and so forth. The role of a custodian in such a case would be to:
- hold in safekeeping assets/securities such as stocks, bonds, commodities such as precious metals and currency (cash), domestic and foreign
- arrange settlement of any purchases and sales and deliveries in/out of such securities and currency
- collect information on and income from such assets (dividends in the case of stocks/equities and coupons (interest payments) in the case of bonds) and administer related tax withholding documents and foreign tax reclamation
- administer voluntary and involuntary corporate actions on securities held such as stock dividends, splits, business combinations (mergers), tender offers, bond calls, etc.
- provide information on the securities and their issuers such as annual general meetings and related proxies
- maintain currency/cash bank accounts, effect deposits and withdrawals and manage other cash transactions
- perform foreign exchange transactions
- often perform additional services for particular clients such as mutual funds; examples include fund accounting, administration, legal, compliance and tax support services
Custodian banks are often referred to as global custodians if they safekeep assets for their clients in multiple jurisdictions around the world, using their own local branches or other local custodian banks with which they contract to be in their "global network" in each market to hold accounts for their respective clients. Assets held in such a manner are typically owned by larger institutional firms with a considerable amount of investments such as banks, insurance companies, mutual funds, hedge funds and pension funds.
Local custodian bank 
In relation to American Depositary Receipts (ADRs), a local custodian bank (also known as a sub-custodian or agent bank) is a bank in a country outside the United States that holds the corresponding amount of shares of stock trading on the home stock market represented by an ADR trading in the U.S, with each multiple representing some multiple of the underlying foreign share. This multiple allows the ADRs to possess a price per share conventional for the US market (typically between $20 and $50 per share) even if the price of the foreign share is unconventional when converted to US dollars directly. This bank acts as custodian bank for the company that issues the ADRs in the U.S stock.
The following companies offer custodian bank services:
- Asia Pacific Banking Investment Group
- Banco de Oro Unibank
- Bank of America
- Bank of China (Hong Kong) Limited
- Bank of Ireland Securities Services
- Bank of New York Mellon
- BBVA Compass
- BNP Paribas Securities Services
- Brown Brothers Harriman
- CIBC Mellon
- Comerica Bank
- Credit Suisse
- Deutsche Bank
- Estrategia Investimentos
- Fifth Third Bank
- Goldman Sachs
- HDFC Bank
- ICICI Bank
- Japan Trustee Services Bank
- JPMorgan Chase
- Kasbank N.V.
- Mitsubishi UFJ Trust and Banking Corporation
- Morgan Stanley Smith Barney
- Northern Trust
- PT. Bank Central Asia, Tbk.
- RBC Dexia
- Societe Generale Securities Services
- Standard Bank
- Standard Chartered Bank
- State Bank of India
- State Street Bank and Trust Company
- The Kingdom Trust Company
- The Master Trust Bank of Japan
- U.S. Bank
- Union Bank N.A.
- Wells Fargo Bank
Self-directed retirement account custodians 
Not to be confused with securities safekeeping custodians, in the U.S., various retirement plan investment accounts require "custodians" which have only a notion of safekeeping or possession in the concrete sense that securities or assets are custodied, but, rather, this arrangement is more about recordkeeping and administration than holding of invested assets. True, a custodian bank could also happen to be a retirement account administrator/"custodian", though a commercial bank could also be such a "custodian" and not be a "custodian bank". Such financial institutions specialize in the administration and 'custody' of individual or self-directed retirement plan such as IRAs, Roth IRAs, SEP IRAs, Rollover IRAs and Solo 401(k)s. Such institutions provide required legal custody services for the assets associated with self-directed retirement plans and administrative services such as investment execution, recordkeeping, accounting, and IRS and client reporting, while the actual account investments are held or custodied in accounts elsewhere.
Mutual Fund Custodian 
A Mutual Fund Custodian refers typically to a custodian bank or trust company (a special type of financial institution regulated like a "bank"), or similar financial institution responsible for holding and safeguarding the securities owned by a mutual fund. A mutual fund's custodian may also act as one or more service agents for the mutual fund such as being the fund accountant, administrator and/or transfer agent which maintains shareholder records and disburses periodic dividends or capital gains, if any, distributed by the fund. The vast majority of funds use a third party custodian as required by SEC regulation to avoid complex rules and requirements about self-custody.
A mutual fund retirement account (IRA, SEP etc.) custodian, however, refers to the plan administrator and recordkeeper such as noted above, which may not necessarily be the same institution providing custody services to the investments of the overall fund.
See also 
- "Bank of China (Hong Kong) Ltd". Bochk.com. Retrieved 2012-09-28.
- "Estrategia Investimentos". Estrategia Investimentos. Retrieved 2012-09-28.
- "KAS BANK – European Specialist in Securities Servicing". Kasbank.com. 2012-08-30. Retrieved 2012-09-28.
- "Kingdom Trust-Institutional Custody for RIAs/Investment Sponsors". Kingdomtrustco.com. Retrieved 2012-09-28.