  Alfred Tarski (1901–1983) described himself as “a mathematician (as well as a logician, and perhaps a philosopher of a sort)” (1944, p. 369). He is widely considered as one of the greatest logicians of the twentieth century (often regarded as second only to Gödel), and thus as one of the greatest logicians of all time.  Among philosophers he is especially known for his mathematical characterizations of the concepts of truth and logical consequence for sentences of classical formalized languages, and to a lesser extent for his mathematical characterization of the concept of a logical constant for expressions of those same languages. Among logicians and mathematicians he is in addition famous for his work on set theory, model theory and algebra, which includes results and developments such as the Banach-Tarski paradox, the theorem on the indefinability of truth (see section 2 below), the completeness and decidability of elementary algebra and geometry, and the notions of cardinal, ordinal, relation and cylindric algebras. After a biographical sketch, this entry offers a condensed exposition of the parts of Tarski’s work that are most relevant to philosophy, his theories of truth, logical consequence and logical constants. In this exposition we have attempted to remain as close as possible to Tarski’s original presentations, reducing to a minimum the number of claims that might be controversial philosophically or exegetically. The final section on further reading refers the reader to other entries and works on critical and exegetical aspects of Tarski’s work not touched upon in this entry.