Oligopolies and monopolies are very important ways of obtaining income without providing a productive service. They produce goods, a productive service. However, they receive additional income by raising prices, and their oligopoly/monopoly profits are distinguished by economists from normal profits and other expenses, which are the returns to productive activity. There are other harmful aspects to concentration and large firms as well, including restriction of innovation, using patents to defend market position, non-compete requirements for their employees, and substantial political power.  Also see Obtaining income from the government as both are often involved. Tax havens are another way in which taxes can be minimized and income from corruption can be laundered.