Kurt Go del first published his celebrated theorem, showing that no axiomatization can determine the whole truth and nothing but the truth concerning arithmetic, nearly a century ago. It challenged prevalent beliefs about the nature of mathematics, and raised significant philosophical questions. This Very Short Introduction gives a clear statement of the theorem, places it in its intellectual and historical context, explains the key concepts involved in it, and scotches some common misunderstandings of it. Moore also provides two proofs, each highlighting something distinctive about its content--back cover.