Having Accounts With Other Ad Advertisers

The old saying “Don’t put all your eggs in the same basket” applies to ads on your site.

You can participate in other ad programs, but you are not permitted to display Google ads on web pages containing competing ads. This includes all content-targeted ads as well as text based ads. Text based ads are ads that copy Google ads or that may appear to be associated with Google ads on other pages of your site. Affiliate or limited text links are not permitted either. None of the ads from other programs can contain any advertisements in common with another
ad unit.

You cannot, however, sign up for more than one Google AdSense account.