In a few short paragraphs of The Problems of Philosophy Bertrand Russell presents his theory of introspective knowledge based on the concept of knowledge by acquaintance. In this article, I critically analyze these comments by Russell and their proposed application by contemporary authors, including Brie Gertler (2001; 2011) and Laurence BonJour (2003). I show how these theories differ from the competing ‘inner‑sense theories’ and try to show that they are inconsistent with Gareth Evans’s ‘transparency’ observation. Then I compare acquaintance theories with Alex Byrne’s (2005; 2012) ‘transparency’ theory and show that Byrne’s theory offers a simpler account of mechanisms governing introspection and attribution of mental states to other agents than the observer.