Each country has it’s own regulator for the use of drones. Regulation of drones that are Remotely Piloted Aircraft almost always comes under the aviation rules of a country. As this is a developing field, regulators often struggle to keep up with the technology.
It is extremely important that you understand and follow the rules in your country as in some cases there are sever penalties for not obeying the rules. Here is a list of countries, and links to the relevant regulator, and some contact details.