To log in to your Mastercard credit card account, go to the login page on the issuer’s website or mobile app and enter your username and password in the appropriate fields. Then, click the login button to access your online account. If you don’t already have an online account, you can start by clicking the option to register your card online, then set up a username and password with your credit card’s issuer. How to Log in to a Mastercard Account Online Register your Mastercard credit card for online account access. Look for and click the option to register your card on the issuer’s login page and enter your info to verify your credit card account. Choose your username and password. Requirements will vary depending on the issuer. An issuer’s username and password may be case-sensitive, have a minimum or maximum character count, or require numbers and/or special characters. Log in with your new credentials. From the login page on the issuer’s website or mobile app, fill out the username and password fields using your new credentials, then click the login button to access your account. After you have signed up and logged in, you’ll be able to manage your Mastercard credit card account online. You can pay your credit card bill, see credit card statements, monitor account activity, and change account information such as passwords and automatic payments. If you forgot your login information, click the link on the issuer’s login page to reset your credentials. Then, just follow the prompts to reset or retrieve your username or password. Note that you cannot log in to your credit card account directly from the Mastercard website. Answer from Chip Lupo on wallethub.com