Not that kind of cardboard!
Although it's made of cardboard, pizza boxes are NOT recyclable. We all love the cheesy, greasy, good stuff, but that's the same reason we can't recycle pizza boxes. The grease and cheese stain the cardboard putting it in the contamination category.
If you're a recycling superstar...
You can rip off the top part, that isn't stained with grease, and recycle that.