Problems of social choice frequently take the following form. There are n voters and a set K = (1,2,…,k) of objects. The voters must choose a subset of K. We deﬁne a class of voting schemes called voting by committees. The main result of the paper is a characterization of voting by committees, which is the class of all voting schemes that satisfy voter sovereignty and non-manipulability on the domain of separable preferences. This result is analogous to the literature on the Groves and Clarke scheme in that it characterizes all of the non-manipulable voting schemes on an important domain.