3D Secure authentication is a security protocol designed to provide an additional layer of security for online credit and debit card transactions. It is an extra step that customers can enable to happen every time a card transaction is made online, which enhances security measures for shoppers and vendors alike. When 3D Secure is triggered, the customer is directed to an authentication page on their banks website, where they enter a password associated with the card or a code sent to their phone. This process is familiar to customers through the card networks brand names, such as Visa Secure and Mastercard Identity Check.

The name 3D comes from the three-domain model used to provide the additional layer of secure authentication between the financial authorization process and online authentication process. The three domains used to provide this security are the acquirer domain, the issuer domain, and the interoperability domain. 3D Secure uses XML messaging and SSL communication to secure and authenticate transactions.

3D Secure is optional in some regions but is required by law in others, such as the Strong Customer Authentication regulation in Europe. It is used extensively in the EU, Australia, India, Brazil, Mexico, Singapore, and other countries. If a customer receives a "3D Authentication failed" error, it means that they have not entered the required information successfully, and they should double-check for typing errors or contact their credit card issuer for additional information.