AI Memo No. 453, May 1978. The Art of the Interpreter, or The Modularity Complex. Guy L. Steele and Gerald Jay Sussman.
This influential paper/essay starts with an description of the history of the Lisp programming language, then continues by describing a series of language features, and how they are motivated by the need to support modular programming.
What made it groundbreaking is the fact that each of these features are described through a small interpreter implementing it, so-called metacircular evaluators. The elegant manner this in done in is a wonderful demonstration of Steele and Sussman's master-hackerdom -- more than two decades later, the essay is still a very worthwhile read.
Most of the ideas in this paper were later worked into the textbook Structure and Interpretation of Computer Programs by Sussman and Harold Abelson, so readers of that book will find them familar. As in SICP, the language used is Scheme.
The Art of the Interpreter can be downloaded as a scanned PDF from the MIT Artificial Intelligence Lab's online bibliography: http://www.ai.mit.edu/publications/pubsDB/pubsDB/onlinehtml