The signaling (or cueing) principle, refers to the finding that multimedia learning materials become more effective when cues are added that guide learners’ attention to the relevant elements of the material or highlight the organization of the material. In this chapter, the main findings from research on signaling in multimedia learning are reviewed, addressing the effects of incorporating cues into the text, the picture, or both. In addition, the design of cues based on the eye movements of successful students and the effects of using experts’ or students’ eye movements as cues are discussed. This chapter shows that various types of cueing can have beneficial effects on learning.