By celebrity, I mean maybe a famous singer.
If they are doing a world tour, they are doing "work" in many countries around the world. From my understanding, in most countries if you want to "work", you must have some sort of permit.
I also know that it depends on the type of work you will be doing. For example, in Canada, if you are working as an athlete or coach , you do not need a permit.
What about singers/actors/filmmakers? Do they require work visas to most countries they visit?