How do you keep a pot from boiling over?

Last night, I was making macaroni and for awhile all was going well. Then the pot started boiling over, so I took the lid off. And, yet, the pot still boiled over onto the stove eye. I had to end up taking the pot off the stove. It was a real mess. I like to use a pot lid, while cooking to keep the cats out of my food, but inevitably the food boils over. How do you keep your pots from boiling over while you're cooking? Are there ways to cook food on the stove, while using a lid, without the water boiling over? Would appreciate suggestions.