 The liar paradox is a significant barrier to the construction of formal theories of truth as it produces inconsistencies in these potential theories. A substantial amount of research in self-reference concentrates on formal theories of truth and ways to circumvent the liar paradox. There are two articles that have influenced the work on formal theories of truth and the liar paradox more than any other: Alfred Tarski’s “The Concept of Truth in Formalised Languages” (1935) and Saul Kripke’s “Outline of a Theory of Truth” (1975). Below we first introduce some of the ideas and results of Tarski’s article. Kripke’s article is discussed in Section 3.2.