and exchange was cited in Clause IV of its constitution as a goal of the British Labour Party and was quoted on the back of its membership cards. The clause read: To secure for the workers by hand or by brain the full fruits of their industry and the most equitable distribution thereof that may be possible upon the basis of the common ownership of the means of production, distribution and exchange, and the best obtainable system of popular administration and control of each industry or service. Antitrust economics In antitrust economics, common ownership describes a situation in which large investors own shares in several firms that compete within the same industry. As a result of this overlapping ownership, these firms may have reduced incentives to compete against each other because they internalize the profit-reducing effect that their competitive actions have on each other. The theory was first developed by Julio Rotemberg in 1984. Several empirical contributions document the growing importance of common ownership and provide evidence to support the theory. Because of concern about these anticompetitive effects, common ownership has "stimulated a major rethinking of antitrust enforcement". The United States Department of Justice, the Federal Trade Commission, the European Commission, and the OECD have all acknowledged concerns about the effects of common ownership on lessening product market competition. Contract theory Neoclassical economic theory analyzes common ownership using contract theory. According to the incomplete contracting approach pioneered by Oliver Hart and his co-authors, ownership matters because the owner of an asset has residual control rights. This means that the owner can decide what to do with the asset in every contingency not covered by a contract. In particular, an owner has stronger incentives to make relationship-specific investments than a non-owner, so ownership can ameliorate the so-called hold-up problem. As a result, ownership is a scarce resource that should not be wasted. In particular, a central result of the property rights approach says that joint ownership is suboptimal. If we start in a situation with joint ownership (where each party has veto power over the use of the asset) and move to a situation in which there is a single owner, the investment incentives of the new owner are improved while the investment incentives of the other parties remain the same. However, in the basic incomplete contracting framework the suboptimally of joint ownership holds only if the investments are in human