Can you have more than just Google AdSense ads on your Web pages?

I think very highly of the Google AdSense program (read my article Get Started with Google AdSense to learn more about the program and how it can easily help you begin to monetize your current Web traffic) and am always interested in hearing questions from others about how it works and the nuances of being a member of the AdSense network, so I was unsurprised when I received a fairly common question in the mail a few days ago:

    Does Google AdSense allow other advertising?

The answer is "yes", but there's a very important caveat that you need to know lest you get kicked out of the AdSense program by having the wrong additional adverts appearing on your pages.