Children and teenagers across England and Wales have been banned from using sun-beds.
The new law will stop under 18s from getting a tan on the beds in places like gyms and salons.
And the punishment for breaking the rules is pretty big - tanning shops could be fined £20,000 if they're caught letting kids use the beds.
A leading health charity says the new law will help protect children from developing skin cancer in later life.
The law was passed last year but it comes into force today.