To assist textbook adoption committees in answering the questions that arise as they consider basal reading series, this paper provides a discussion of readability. Following a brief introduction, the second section of the paper offers a background discussion of what readability really means. In addition, this section looks at three factors to consider in judging the difficulty level of a book and discusses the various ways textbook difficulty can occur. The third section of the paper discusses the usefulness of readability formulas in evaluating textbook materials, concluding that they are most successful when applied to passages that are well-organized, appropriately written, and free of unusual vocabulary and sentence constructions. The fourth section of the paper explains what to look for in determining text difficulty and how to look for it. (FL)