I have chosen this topic in my thesis, because in my opinion, offshore companies still play a major role in the economy. In the first half of my thesis, I discuss tax avoidance in general. In the second half of the thesis, I introduce offshore company types, with the main rules of incorporation in Dominica, Belize, United Arab Emirates, Seychelles, Cyprus and Delaware. Then, regarding offshore companies, I discuss one of the main topics of nowadays, in particular the international information exchange and common actions against tax avoidance performed using offshore companies, introducing the relevant international co-operation. Finally, I summarize the actual situation regarding the international judgment of offshore companies.