DSL Router

I use a Efficient 5600 DSL Router at work. I am getting ready to set my home network up. I have ask the question do you have to have a modem to go along with the router. I have received contridicting answers. The router we use at work does not have a modem with it. I was told it is sorta built-in. It is a $300.00 router, and you can get cheaper ones that are still made by good companies. Can anyone help? Do I have to have a modem to go along with my router. Use the Belkin DSL/Cable router for instance. Thank you for your help.
Stephen