Can I get internet with just a router?

Excuse me, I'm a bit confused about something. I've been thinking about setting up a home network and I was wondering, is it possible to get internet access with just a router? I've heard some people say that you need a modem as well, but I'm not sure if that's the case. Could you please clarify for me? Is a router alone sufficient for internet access, or do I need to get a modem as well? Thank you for your help.