Nondeterministic LISP is a simple extension of LISP which provides automatic backtracking. Nondeterminism allows concise description of many search tasks which form the basis of much AI research. This paper discusses SCREAMER, an efficient implementation of nondeterministic LISP as a fully portable extension of COMMON LISP. In this paper we present the basic nondeterministic LISP constructs, motivate the utility of the language via numerous short examples, and discuss the compilation techniques.