The main goal of this research study was to develop a conceptual model for the design of public library websites for teens (TLWs) that would enable designers and librarians to create library websites that better suit teens' information needs and practices. It bridges a gap in the research literature between user interface design in human-computer interaction (HCI), and library website design studies in library and information science. Compared to studies of children and adults, there are few studies of teens' use of library websites. While the HCI literature provides an abundance of information regarding user interface design, there is limited data on the teen population and their design needs. As a result, current designs of TLWs appear as varied combinations of websites for children and adults with no consistent conceptual model being used to represent the needs and user design preferences of teen users. This study was divided into two parts. In Part I, users' mental models were extracted individually through drawings and semi-structured interviews from 30 teen participants (13-15 years old) recruited from three public libraries in New Jersey. In Part II, a web analysis was performed on 60 U.S. public library TLWs stratified based on the same library population service area of the three libraries in Part I. Both parts combined to develop a conceptual model that will enable designers and librarians to create user interface designs that respond to the needs of teens. The findings revealed five teens' mental models (Single Functional, Process, Social Connection, Portal, Information Discovery) and of those five only two (Portal and Information Discovery) were also identified in the website models. The websites also included two additional models (Reading and Media-oriented). This suggests that the future design of TLWs can benefit from teens' mental models and an understanding of how those mental models are reflected in current TLWs and across the web. Designers of TLWs can benefit from understanding a mapping of teens' mental models to website models and how best to respond to teens' expectations when interacting with TLWs. [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.]