Double Irish arrangement
The Double Irish arrangement was a base erosion and profit shifting (BEPS) corporate tax avoidance tool used mainly by United States multinationals between the late 1980s and late 2010s to avoid corporate taxation on non-US profits. (The US was one of a small number of countries that did not use a "territorial" tax system, and taxed corporations on all profits, no matter whether the profit was made outside the US or not, in contrast to "territorial" tax systems which tax only profits made within that country.) It was the largest tax avoidance tool in history.