How tasks affect users' information-seeking and search behavior has drawn much attention in information science. This research examines the relationships among work tasks, search tasks, and interactive information search behavior. Two sequential studies taking a faceted classification of tasks as a research framework were conducted to examine the relationships. The results indicate that work tasks are significantly associated with search tasks and shape search tasks to a great extent. Work tasks also significantly affect users' interactive information search behavior. This research demonstrates that a faceted approach to conceptualizing tasks is feasible and effective. The research has implications in task-based information seeking and retrieval and personalization of information retrieval. It could be a useful book for graduate students in information science and anyone else who is interested in this area, especially in task and interactive information retrieval.