The purpose of this monograph is to explore the concept of educational adequacy, defined by Cubberley as "a generous system of free public schools," and to apply those measures in an analysis of educational adequacy in the state of Illinois. The difficulty in defining what constitutes a generous education is that there is no clear consensus in American society on what schools should achieve. Accordingly, this paper begins with a discussion of basic issues and standards in American public education and outlines three approaches to adequacy, based on school inputs (resources, standards), school outputs (test scores, graduation rates), and school outcomes (economic returns to education, good citizenship). Subsequent sections apply these general concepts of adequacy to an analysis of the Illinois State system of education. Included are functional measures of educational adequacy in Illinois as compared with other states and national averages, followed by a review and analysis of public school funding in Illinois during the past two decades. The last two sections address the relationship between adequacy and equity in Illinois school finance and public policy implications of the foregoing analysis of educational adequacy in Illinois. Notes are provided, along with three sets of statistical tables and charts showing (1) public school revenues in relation to personal income in Illinois and the United States in recent years; (2) per pupil receipts for Illinois public schools 1967-68 and 1986-87; and (3) Illinois public school average per-capita tuition charge by district type, 1976-77 to 1984-85. (TE)