It has been argued that the Swedish tax system has favored firm control through industrial foundations, which should have inhibited entrepreneurship and economic growth. However, research has been hampered due to a lack of systematic historical tax data. The purpose of this study is to describe the evolution of tax rules for industrial foundations in Sweden between 1862 and 2018 and to calculate the marginal effective tax rate on capital income (METR). The results show that the METR for an equity financed investment is below 20 percent most of the time and occasionally peak at about 40 percent. Treating the requirement that industrial foundations have to donate the bulk of capital income (less capital gains) to charitable purposes as a tax, the METR seldom is below 50 percent when financing investments with new share issues, and often exceeds 100 percent.