A safe deposit box, sometimes known as a safety deposit box, is an individually secured container, usually held within a larger safe or bank vault. Safe deposit boxes are generally located in banks, post offices or other institutions. Safe deposit boxes are used to store valuable possessions, such as gemstones, precious metals, currency, marketable securities, important documents such as wills, property deeds, and birth certificates, or computer data storage that need protection from theft, fire, flood, tampering, or other perils. In the United States, renting out a safe deposit box in a bank does not mean that the property is automatically insured. An individual should still purchase insurance for the safe deposit box in order to cover theft and natural disasters.

In the typical arrangement, a renter pays the bank a fee for the use of the box, which can be opened only with presentation of an assigned key, the bank's own guard key, the proper signature, and sometimes a code of some sort. Some banks additionally use biometric dual-control security to complement the conventional security procedures. The security measures utilized by many institutions often make safe deposit boxes a poor repository for wills, powers of attorney and other estate planning documents if the owner has not authorized additional signatories on the account.