The presentation of several sources of information through different, sensory modalities in multimedia environments has great potential for promoting meaningful learning. However, multimedia learning sometimes fails to live up to its full potential, because high cognitive loads are often generated, primarily by the requirement to integrate different sources of information. We argue that. measurement of cognitive load is needed for researchers and designers to be able to engineer the instructional control of this high cognitive load and design effective multimedia learning environments. This chapter describes die theoretical background for the assessment of cognitive load in multimedia learning environments, different methods for assessing copitive load, practical examples to demonstrate how cognitive load can be assessed in those environment, and how such assessments can inform the instructional design process.