This document provides an overview on how and why EGR coolers are utilized@ defines commonly used nomenclature@ discusses design issues and trade-offs@ and identifies common failure modes. The reintroduction of exhaust gas into the combustion chamber is just one component of the emission control strategy for internal combustion (IC) engines@ both diesel and gasoline@ and is useful in reducing exhaust port emission of Nitrogen Oxides (NOx). Other means of reducing NOx exhaust port emissions are briefly mentioned@ but beyond the scope of this document.