To help clarify the role of urban main libraries, visits were made to nine library systems serving populations of 500,000 to 750,000 for the purpose of exploring: (1) system priorities; (2) budgetary support for materials; (3) public service staff; and (4) materials selection procedures. Particular emphasis was placed upon the financial and functional relationships between the systems' main and branch libraries. The public library systems visited were: Memphis/Shelby County, Louisville, Indianapolis-Marion County, Kansas City, St. Louis, Salt Lake County, Phoenix, New Orleans, and Atlanta. Each system's priorities and functional relationships are enumerated, including data concerning materials budgets and a list of persons interviewed. Results of the study show that: (1) library automation, budgets, and staff and volunteer programs were the most frequently cited priorities; (2) 40 to 59 percent of the total material was distributed among the branches and other extension services; (3) there is an emphasis on hiring and assigning librarians with subject expertise to the main library, while the branch personnel are selected for their expertise in general public services work; and (4) the selection of new and replacement adult materials for the main libraries rests primarily with the department heads. A list of main and branch library functions concludes the report. (JPF)