As Wikipedia defines it, “two-factor authentication provides unambiguous identification of users by means of the combination of two different components.” In practice, this means you need to prove you are who you say you are in two different ways.
Usually two factor authentication with a registrar involves a username/password pair *and* an authentication code retrieved from your mobile phone, which has been associated with your account.
Below is an alphabetical listing of domain name registrars that provide two factor authentication, along with some application notes. Be aware that your domain names are valuable assets and you should use two factor authentication to protect your account and domain names.
Dotology.com: Two-factor Authentication (no public info, go to Settings > Account Settings) (Google Authenticator app)
GoDaddy.com: Enabling Two-Step Authentication for Your GoDaddy Account (SMS only, USA-based SMS only)
Lexsynergy.com: (Google Authenticator app)
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