Suppose I gave an artist a free beat (music instrumental) that was copyrighted and he uses it and makes money off of it. All he does is add his vocals to my copyrighted beat and calls the song his own.

What can I do?

Did you register for a copyright online / mail or is it just "protected" because of intellectual property law? Regardless, what were the terms of the transaction? It's civil law not criminal, so you can't do anything but sue him for a part of the money he has made. Then you would have to prove that you not only made the track but also gave it to him under the terms that you still owned the copyright and he could not use it for production. And if he isn't making much money off it then it wouldn't even be feasible to squabble over hit.

The terms were he would use the beat for free and that its a good thing if my beat is heard on a mixtape featuring major artists. He's not a major artist but the mixtape he's on contains a few features. Hes not making a fortune. I registered for it online.

I gave him permission to use it so...it doesnt make a difference if its copyright or not?