In a multiparty message-passing model of communication, there are k players. Each player has a private input, and they communicate by sending messages to one another over private channels. While this model has been used extensively in distributed computing and in multiparty computation, lower bounds on communication complexity in this model and related models have been somewhat scarce. In recent work [40,46,47], strong lower bounds of the form Ω(n · k) were obtained for several functions in the message-passing model; however, a lower bound on the classical Set Disjointness problem remained elusive.In this paper, we prove tight lower bounds of the form Ω(n · k) for the Set Disjointness problem in the message passing model. Our bounds are obtained by developing information complexity tools in the message-passing model, and then proving an information complexity lower bound for Set Disjointness. As a corollary, we show a tight lower bound for the task allocation problem [19] via a reduction from One of the most natural application domains for communication complexity is distributed computing: When we wish to study the cost of computing in a network spanning multiple cores or physical machines, it is very useful to understand how much communication is necessary, since communication between machines often dominates the cost of the computation. Accordingly, lower bounds in communication complexity have been used to obtain many negative results in distributed computing, from the round complexity of finding a minimum-weight spanning tree [42] to computing functions of distributed data [37,29] and distributed computation and verification of network graph structures and properties [42,23].To the best of our knowledge, however, all applications of communication complexity lower bounds in distributed computing to date have used only two-player lower bounds. The reason for this appears to be twofold: First, the models of multi-party communication favored by the communication complexity community, the number-on-forehead model and the number-in-hand broadcast model, do not correspond to most natural models of distributed computing. Second, two-party lower bounds are surprisingly powerful, even for networks with many players. A typical reduction from a two-player communication complexity problem to a distributed problem T finds a sparse cut in the network, and shows that, to solve T , the two sides of the cut must implicitly solve, say, Set Disjointness [30]. However, there are problems that cannot be addressed by reduction from a two-player problem, because such reductions must reveal almost the entire structure of the network to one of the two players. (One such example is described in [29].)In this paper, we study communication complexity in message-passing models, where each party has a private input, and the parties communicate by sending messages to each other over private channels. These models have been used extensively in distributed computing, for example, to study gossiping protocols [27], to compute various functions...