Richard Ludwig Heinrich Avenarius (19 November 1843 – 18 August 1896) was a German-Swiss philosopher.

At the University of Leipzig, he received the Doctor of Philosophy in 1868 with his thesis on Baruch Spinoza and his pantheism, obtained the habilitation in 1876 and taught there as Privatdozent.

Avenarius believed that scientific philosophy must be concerned with purely descriptive definitions of experience, which must be free of both metaphysics and materialism.

Avenarius' principal works are the famously difficult Kritik der reinen Erfahrung (Critique of Pure Experience, 1888–1890) and Der menschliche Weltbegriff (The Human Concept of the World, 1891) which influenced Ernst Mach, Ber Borochov and, to a lesser extent, William James.

[2] He taught Anatoly Lunacharsky and was also influential on Alexander Bogdanov and Nikolai Valentinov.