Those interested in textbook research, theory, and practice need to identify the independent or context variables that influence the making of a textbook--the intervening variables that come into play as textbooks are conceived, developed, and designed--and to show how these impact on the textbook, or dependent variable. To begin, critics and researchers need to be sure they are talking about the same thing when they discuss the textbook. Further, they need to agree on those characteristics that distinguish educational books from all others. Textbook innovation can then be examined through a conceptual framework that identifies three levels of gatekeepers that affect the innovation process: (1) primary gatekeepers (publishers); (2) secondary gatekeepers (editors, authors, writers, consultants, and salespeople); and (3) tertiary gatekeepers (knowledge producers such as out-of-house consultants, the government, the general public, educators, and textbook researchers). Such a systems view of gatekeeping and the monitoring of innovations suggest that publishers simply input the outputs of other systems as they pursue the legitimate objectives of the knowledge distribution system, namely the distribution of knowledge for profit. If there is to be a change in the quality of textbooks, the input from the tertiary gatekeepers needs to be carefully scrutinized, since the use of readability formulas (an output of the tertiary gatekeepers) has contributed to the "dumbing down" of textbooks. (HOD)