Mobile eye-tracking is a technology that captures visual information, such as gaze, eye-movements, and pupil dilations, when learners are mobile. Traditional eye-tracking helps researchers to obtain precise, moment-by-moment information about learners’ engagement, interactions, and learning processes. Still, it has some weaknesses due to its structural and stationary nature. Mobile eye-tracking can complement such weaknesses by allowing researchers to collect eye-tracking data when learners move around and interact with multiple targets. This chapter demonstrates how mobile eye-tracking can add more authenticity and nuanced information into Learning Design and Technology research, and then introduces potential research themes that can use mobile eye-tracking. This chapter also overviews the overall processes of applying mobile eye-tracking in a research study and provides an example analysis.