I develop a model of decision making in juries when there is uncertainty about jurors' preferences. I provide a characterization of the equilibrium strategy under any voting rule and show that nonunanimous rules are asymptotically efficient. Specifically, large juries make the correct decision with probability close to one. My analysis also demonstrates that under the unanimous rule, large juries almost never convict the defendant. The last result contrasts markedly with the literature and suggests that the unanimity rule can protect the innocent only at the price of acquitting the guilty.