> For the complete documentation index, see [llms.txt](https://fusionauth.io/docs/llms.txt)

# Pre-1.26 2FA

Learn how to complete a Two-Factor authentication for a User.

> **CAUTION:** The functionality described on this page is deprecated as of version `1.26.0`. For `1.26.0` and later, see the [Email & Messages documentation](https://fusionauth.io/docs/customize/email-and-messages.md).

Two-Factor authentication adds an additional step to the authentication process. In addition to requiring a valid email and password to authenticate, a two-factor authentication code is required.

The general idea of Two-Factor authentication is to require something you know and something you have to complete authentication. Using this pattern protects the User against having their credentials compromised because even if you ***know*** someone's email and password, unless you also possess the device that generates the two-factor authentication code you are not able to complete an authentication process. In most cases the device the user will possess will be a mobile phone.

*   [Two-Factor using Google Authenticator (or similar application)](https://fusionauth.io/docs/customize/email-and-messages/deprecated/authenticator-app-pre-1-26.md)
*   [Two-Factor using Twilio Push Notifications](https://fusionauth.io/docs/customize/email-and-messages/deprecated/twilio-push-pre-1-26.md)