In Park and Brünken (2015), we already concluded from the current state of cognitive load research that the usefulness of cognitive load theory (CLT) as a framework is impressively confirmed. However, a necessary systematic investigation to test and compare different methods for measuring cognitive load has not been the focus of cognitive load research until today, with some exceptions (Korbach, Brünken, & Park, 2016, 2017; Leppink, Paas, van Gog, van der Vleuten, & van Merriënboer, 2014; Paas & van Merriënboer, 1993, 1994; Park, Korbach, & Brünken, 2015; Zheng & Cook, 2012). The focus of the present chapter is a summary of research over the last decades on different objective cognitive load measures that were used in learning studies, specifically those incorporating the dual-task paradigm. The use of the dual-task paradigm in order to objectively measure cognitive load during the ongoing learning process requires participants to perform two tasks simultaneously. In studies investigating learning processes, the primary task is the given learning task, for instance, having to read and understand an instruction with including textual and pictorial parts about a complex learning content, such as the structure and function of the human heart, and detailed explanations on how the human cardiovascular system works. Applying the dual-task paradigm in those learning situations leads to the secondary-task paradigm, as a secondary task has to be executed in parallel to the primary learning task. Cognitive load can consequently be measured by the performance of the given secondary task.