Drones regulation is quickly evolving with a notable increase in complexity as more mission types appear, technology advances and public acceptability evolves. Complying with the regulation is complexe enough in a single country, and it gets even more complex for cross-border missions.
To help drone operators in finding the right rules for the right countries, the European Union created a website: dronerules.eu, providing precious information about different regulations across the E.U countries. Though it is not operational yet, there is no doubt it will soon become an essential tool for drone operators.
On a more global scale, the ICAO is providing a UAS toolkit. Though it is oriented towards state regulators, to help them develop their regulation, anyone can use the available links to the regulation of 29 countries around the world.