Ethics, Demonstrated in Geometrical Order (Latin: Ethica, ordine geometrico demonstrata), usually known as the Ethics, is a philosophical treatise written by Benedict de Spinoza. It was written between 1664 and 1665 and was first published in 1677.

The book is perhaps the most ambitious attempt to apply the method of Euclid in philosophy. Spinoza puts forward a small number of definitions and axioms from which he attempts to derive hundreds of propositions and corollaries, such as "When the Mind imagines its own lack of power, it is saddened by it", "A free man thinks of nothing less than of death", and "The human Mind cannot be absolutely destroyed with the Body, but something of it remains which is eternal."