Ireland's Corporate Tax System is a central component of Ireland's economy. In 2016–17, foreign firms paid 80% of Irish corporate tax, employed 25% of the Irish labour force (paid 50% of Irish salary tax), and created 57% of Irish OECD non-farm value-add. As of 2017, 25 of the top 50 Irish firms were U.S.–controlled businesses, representing 70% of the revenue of the top 50 Irish firms. By 2018, Ireland had received the most U.S. in history, and Apple was over one–fifth of Irish GDP. Academics rank Ireland as the largest tax haven; larger than the Caribbean tax haven system.