A survey of the current research on readability formulas is presented in this paper, which distinguishes this research from research on the more general questions that surround formulas: What features of a text, particularly the language it is written in, make the text easy or difficult to read? and, What will predict that readers with particular levels of skills can read a particular text? It then discusses the features of readability formulas that have made them useful and appealing. The next section reviews research that illustrates the inappropriateness or lack of usefulness of readability formulas in cases involving (1) coping with jury instructions and government relations and forms, (2) matching children's books with readers of the right age and level of ability, and (3) choosing school materials of appropriate levels in languages very unlike English. The last sections explore research on readability formulas, addressing the issue of what constitutes complexity of language, and raise the question of which measures of language processing are most sensitive to features of language, and why. Four pages of references are included. (EL)