Abstract: In his Problems of Philosophy, Bertrand Russell distinguished knowledge by acquaintance and knowledge of truths. This paper argues for a new interpretation of the relationship between these two species of knowledge. I argue that knowledge by acquaintance of an object neither suffices for knowledge that one is acquainted with the object, nor puts a subject in a position to know that she is acquainted with the object. These conclusions emerge from a thorough examination of the central role played by attention in Russell’s theory of knowledge. Attention bridges the gap between knowledge by acquaintance and our capacity to form judgements about the objects of acquaintance.