Reinhold's Letters on the Kantian Philosophy is arguably the most influential book ever written concerning Kant. It propelled Kant's Critical Philosophy, which had previously enjoyed an equivocal reception, into the central position which it has held to this day. It also brought fame to Reinhold, who became a professor at Jena and later developed his own "Elementary Philosophy". This volume presents the first English translation of the work, together with an introduction that sets it in its philosophical and historical contexts.