Several years ago a professor at a large research institution prepared to deliver her first on-line course. The activities had been planned meticulously, the software to be used had been tested, and hopes were high. One week after the course started, the professor in frustration pulled students back into the classroom and delivered the course in its traditional format. The problem? The students were unable to figure out how to use the software. This story highlights the need to design Web-based learning experiences that are user-friendly, as well as instructionally sound. While most instructional developers acknowledge the importance of the systematic design process for effective mediated learning experiences, many fail to recognize the necessity to include interface design as a component of that process. Many instructional designers believe that if one can design instruction, one can design anything, including intuitive and easy-to-use Web-based programming. The field of human-computer interaction has evolved over the past 20 years as a discipline of its own, with principles and practices based on empirical research. Though similar to the process of instructional design, interface design is a separate endeavor with its own procedures and outcomes, and is essential to producing good instructional software. In this chapter we will describe how interface design can be integrated into the traditional instructional design process, thereby helping to ensure the overall effectiveness of the final product.