This research examined the functions and roles of public library systems in New York State and the services they provide for individual libraries and the public. The dissertation further studied the service decision-making processes at three selected New York State cooperative public library systems. Public library systems have played an important role in enhancing and expanding library services in the United States since the 1940s, but few existing studies on public library systems focus on their organizational processes. It is the purpose of this research to fill this knowledge gap by conducting a two-stage study in New York State. Since establishing and funding public library systems is not a common practice across all states, it was best to focus the study on one state. This study selected New York State for its well-established public library systems. These public library systems ensure all populations and areas in New York State have access to high quality library services. Stage I of the study used existing data collected by the New York State Library and information on its website to examine 1) the expected roles and functions of public library systems defined in the New York State Education Law and Regulations of the Commissioner of Education; 2) the expressed roles and functions in public library systems' organizational mission statements and five year Plans of Service documents; 3) the actual service features reflected in 2008-2009 public library systems' annual reports. Stage II of the study was multiple case studies on service decision-making processes. Three cooperative public library systems were selected based on findings at Stage I of the study. Interviews were conducted at each public library system with staff members, members of boards of trustees or directors of member libraries. Findings from Stage I of the study identified differences across three different types of public library systems in New York State in the way their expressed roles and functions corresponding to the law and regulations. Variations of service activities exist across all public library systems and are correlated to the "size" of the public library system and its member composition. Public library systems with small and poor member libraries tend to provide more direct support services; public library systems with rich and large member libraries tend to provide more coordinated services. Stage II of the study found that service decision-making processes at each public library system varied based on service contents and organizational capabilities of both the public library system and its members. Findings from this study will add knowledge and information about public library systems, their services and decision-making processes. Findings can also add to the research topic of organizational decision-making processes. Public library systems can use this information to improve their service decision-making processes. Policy makers can use this information to make informed policy and funding decisions to facilitate public library systems' service decision-making processes. Information and library professionals can understand public library systems' service decision-making processes better to participate in the process and to advocate for better services. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]