it's how they figure out the boundaries of behavior. For grown ups it's frustrating, but you can make it less so by being consistent and clear with what's expected.

Tell him what you expect of him, and what will happen if he doesn't follow your rules. Then follow through. It's hard. Trust me -- it's more difficult to walk away from an almost filled grocery shopping cart because your kids just had a meltdown and is screaming than it is to simply buy him that chocolate bar he wants. But if you do that, you're rewarding his bad behavior and then he learns that he just needs to make a fuss and make you uncomfortable to get what he wants.

Figure out his buttons -- things he wants and likes, and use those as privileges that you can yank when he misbehaves.

Timeouts are great too -- budget about a minute for every year old your child is. Have them sit quietly away from people/toys/things for that length of time when they misbehave. (This doesn't always work as easily as one would like -- many times I've had to grab my kid and physically restrain his flailing arms and carry him upstairs and hold the door shut until he calmed down enough and stopped screaming so that he could actually do his time out...turned the whole thing into a 40 minute episode by the time it was all done. But in the end he was calm, he had done the time, and we'd talked about what he did that was wrong, and what were some better choices he could make in the future when that happened again.).

The old carrot instead of the stick approach works wonders for kids. Create a sticker chart for all the good things he does, with a reward if he gets so many stickers. I did this for my kid's bedtime routine. My kid always wanted to sleep with me, would argue about bathtime, etc....it just got frustrating for me. So I made a sticker chart -- he got one sticker for taking a bath without it turning into a war, another for brushing his own teeth, one for taking his vitamin, one for going to bed on time, another for going to bed in his own bed, another for STAYING there all night....and if he got three days in a row with 6 stickers each, then he got a prize. He loved it, and it really made the whole process a lot less stressful.

I'm not one for hitting kids, though I've certainly seen some kids who could use a good smack and I have nothing against parents who do occasionally spank. But in general, I think you can accomplish pretty much everything you need to re: discipline without resorting to that.

Good luck -- it's the toughest job you'll ever love!