After 6 years of employment in London, I wanted to be in Germany to be closer to my family.
My UK employer did not want to lose me, so we agreed that I would continue to work for them from Berlin.
Being German I wanted to go back to the German social security system, but we did not know how to do that in Germany if my employer did not have a company there.
We found Adexpat on Google, and by the end of the month my payroll was started, my UK employer did not have to register a business in Germany, and it has been working really well since.