This study examines university students' multitasking with computers and mobile phones in an authentic self-study context, with the primary focus being on off-task multitasking and interruption as precursor to multitasking. The study drew on interviews, observation, and video-stimulated recall to reveal the triggers for and processes of multitasking. It has identified pop-up notifications as the main external interruption and task completion as well as boredom as the internal sources of interruption. The results also pinpointed task as an important dimension associated with both internal and external interruptions. A framework of multitasking triggers was constructed encompassing user, technology and task. The implications of the findings for students, teachers and researchers are also discussed. Implications for practice or policy: (1) Students should ward off the disruptive influence of notifications on phones during study time; (2) Students should have a better sense of the optimal timing for switching attention; and (3) Teachers should strive to provide meaningful, relevant and personalized learning tasks.