Efforts to institutionalize Bloom's Mastery Learning Concept at the City Colleges of Chicago (CCC) are described. Information on the City Colleges and the adaptation of mastery learning are presented, and the growth of the project in five phases beginning in 1972 is sketched. The optimal pattern for mastery learning consists of a series of small units of material, each presented to the student by traditional techniques but followed by a diagnostic quiz, specific correctives, and a parallel diagnostic quiz. This approach to the cognitive side of student learning provides frequent feedback to the student and promotes individualized instruction. Additional techniques are directed at improving students' attitudes about themselves as learners. The program began in 1972-73 with four faculty members, two in mathematics and two in biology. During the Spring 1980 semester the project involved 129 CCC faculty and 229 mastery classes. To encourage teachers to try mastery learning, the project conducts workshops on the practical use of mastery techniques in the classroom, and three credit hours toward salary advancement are granted. Mastery learning materials that workshop participants are required to develop and implement are outlined. Data on student academic performance, attrition, and other measures are compared for mastery classes and regular classes. The evaluation data are presented for each of the five phases of implementation. A recent study is seeking to determine which of the components of Bloom's Mastery Learning Model are most strongly correlated with teaching effectiveness. (SW)