The term 'inferentialism', coined by Robert Brandom, has become a trademark of a certain position in the philosophy of language which claims that meanings identify with inferential roles – a radical departure from more traditional semantic approaches. Independently of this, the term is now cropping up in logic, in connection with positions prioritizing proof-theory over model theory and approaching meaning in logical, especially proof-theoretical, terms. The book brings these two strands together: it reviews and critically assesses the foundations of Brandomian inferentialism; it proposes upgrades; and it clarifies its relationship to inferentialism in logic. Emphasis is laid on clearly articulating the general assumptions on which inferentialism rests, thus elucidating its foundations, followed by discussing the consequences of this standpoint, and then dealing with the most intensive objections raised against the standpoint.