Online instructional design is a relatively new field for librarians. Many librarians have taken on the challenge of creating online library tutorials without the benefit of formal education and training in the field. Librarians can learn much from research in system design, human-computer interaction, and applied psychology, as it relates to the creation of online learning systems. Researchers in these areas believe that people approach online learning systems by making use of a conceptual-or mental-model of the system. Designers' mental models influence the way they create learning systems; students' mental models affect the way they interact with and learn from the system. This article compares and contrasts the mental models of librarians and students as they relate to online library tutorials. These mental models are examined through a review of existing library tutorials, usability studies on various library tutorials, and student interviews about the research and writing process. Analysis of these models demonstrates how undergraduates' mental models vary, often significantly, from the mental models of the librarians who design the online library tutorials. Interpretations of this analysis identify ways in which to design a tutorial for more effective instruction aimed at the undergraduate.