Cognitive load theory (CLT) is gaining increasing importance in the design and evaluation of instruction, both traditional and technology based. Although it is well understood as a theoretical construct, the measurement of cognitive load induced by instructional materials in general, and by multimedia instruction in particular, mainly relies on methods that are either indirect, subjective, or both. Integrating aspects of CLT, working memory research, and cognitive theories of multimedia learning, we describe the conceptual basis and practical implementation of a dual-task approach to the direct measurement of cognitive load in multimedia learning. This computer-based instrument provides a direct and objective measure that overcomes many of the shortcomings of other indirect and subjective methods that will enable researchers to validate empirically theoretical predictions of CLT.