To introduce the republication of Definitional Interpreters for Higher-Order Programming Languages, the author recounts the circumstances of its creation, clarifies several obscurities, corrects a few mistakes, and briefly summarizes some more recent developments.

operational semantics - denotational semantics - interpreter - lambda calculus - applicative language - functional language - metacircularity - higher-order function - defunctionalization - closure - call by value - call by name - continuation - continuation-passing-style transformation - LISP - ISWIM - PAL - Scheme - SECD machine - J-operator - escape - assignment