Social choice and telling the truth

This paper presents a straightforward proof of Gibbard's theorem that any non-manipulable choice rule with at least three outcomes is dictatorial. The proof is similar to proofs of Arrow's impossibility theorem, but does not rely on that theorem. The last part of the paper discusses the relation between Gibbard's and Arrow's theorems. The paper contains no new result, and is intended to make this important area of social choice theory accessible to a wider audience.