This paper investigates the structures of strategy-proof mechanisms in general models of economies with pure public goods. Under the assumptions that the set of allocations is a subset of some finite-dimensional Euclidean space and that the admissible preferencees are continuous and convex, I establish that any strategy-proof mechanism is dictatorial whenever the decision problem is of more than one dimension. Furthermore, I establish a similar result when preference relations also satisfy the additional assumption of monotonicity. These results properly extend the Gibbard-Satterthwaite theorem to economies with pure public goods.

The main result of this paper characterizes voting by committees. There are n voters and K objects. Voters must choose a subset of K. Voting by committees is defined by one monotone family of winning coalitions for each object; an object is chosen if it is supported by one of its winning coalitions. This is proven to be the class of all voting schemes satisfying voter sovereignty and nonmanipulability on the domain of separable preferences. The result is analogous to the characterization of Clarke-Groves schemes in that it exhibits the class of all nonmanipulable schemes on an important domain.