Whether or not you should work out your abs every day is a topic hotly debated in the fitness community. Some professionals claim your abs are just like any other muscle that need recovery time between workouts to stimulate growth. Your abs, however, are relatively unique in how they function. And, unless you're adding significant resistance to your ab routine or working them so hard that they are noticeably sore the next day, you're safe to work them every day. But, just because you can work your abs every day doesn't mean it's the most effective way to attain a strong core, flat abs or lean physique.
The Abdominals are a Unique Muscle Group
Your abs engage regularly during the day -- not just during crunches and leg lifts. They serve as the axis of all your activity -- providing you the ability to stabilize, twist and bend. When you stand tall during lunges, balance on one leg in yoga or maintain good posture during a shoulder press, your abs activate. This means you essentially do "work" them every day already, even without meaning to.