- Vegetables / fruits / roots / herbs
- Meat / seafood / eggs
- Nuts and seeds, in moderation
and generally agreed to exclude:
- Grains (including wheat, rice, corn, etc.)
- Cane sugar and refined sweeteners
- Most legumes
The basic principle is simple: eat things that our bodies are made to handle well, that make us healthy and allow our systems to self-regulate properly. It boils down to eating things that our hunter-gatherer forebears would tend to eat, before becoming agrarian (thus the "paleo" nickname) and well before collectively wrecking our health with the "Western Diet" - however, it's not historical re-enactment, but practical guidelines.
It's not the Atkins diet, nor explicitly low-carb (it does tend to result in low carbs, but that's not the goal), and it doesn't require you to count calories or starve yourself. Given you are eating the right things, you eat when and how much you feel like, and trust your body. Of course, definition and practice vary widely. Some good references to get started are PaleoDiet and Robb Wolf's intro.
Some would see this diet as restrictive. If you're used to the standard American diet and the "food pyramid" we grew up with here, it certainly is. However, we prefer to see it as being creative with healthy ingredients. There are so many good things available that most of us don't pay attention to while eating pizza and drinking soda, and so many people pointing the way to explore those good things (check our blogroll!). We limit ourselves in one direction in order to expand in another.