High demands on learners in Web-based learning environments and constraints of the human cognitive system cause disorientation and cognitive overload. These problems could be inhibited if appropriate cognitive tools are provided to support learners' cognitive processes. The purpose of this study was to explore the factors influencing the use of cognitive tools in Web-based learning environments. This study used data from 31 students who attended a course delivered via the Internet. The students used 9 different cognitive tools developed in accordance with the promises of "cognitive load theory," "mental model theory," and "information processing theory." Data were collected through group interviews and questionnaires. Additionally, computer logs were analyzed to validate qualitative data. Results revealed that such factors as learning strategies, learners' prior knowledge, the usability of and orientation to tools, connectivity cost, and the content influenced learners' utilization of Web-based cognitive tools. (Contains 3 figures and 2 tables.)