A System of Logic, Ratiocinative and Inductive is an 1843 book by English philosopher John Stuart Mill. In this work, he formulated the five principles of inductive reasoning that are known as Mill's Methods. This work is important in the philosophy of science, and more generally, insofar as it outlines the empirical principles Mill would use to justify his moral and political philosophies. An article in "Philosophy of Recent Times" has described this book as an "attempt to expound a psychological system of logic within empiricist principles.”

This work was important to the history of science, being a strong influence on scientists such as Dirac. A System of Logic also had an impression on Gottlob Frege, who rebuked many of Mill's ideas about the philosophy of mathematics in his work The Foundations of Arithmetic.

Mill revised the original work several times over the course of thirty years in response to critiques and commentary by Whewell, Bain, and others.