In the context of instructional design and self-regulated learning research, the notion of mental effort allocation, monitoring, and control has gained increasing attention. Bringing together a cognitive perspective, focusing on Cognitive Load Theory, and a motivational perspective, merging central accounts from Situated Expectancy Value Theory and Self-Determination Theory, we plea for a three-fold conception of effort that clearly distinguishes the different psychological sources of experiencing and allocating effort in learning environments: effort-by-complexity, effort-by-need frustration, and effort-by-allocation. Such a detailed conception has important implications for how effort should be studied and how it can be influenced by instructional support or by the learning individual itself. A first conclusion we draw is that cognitively oriented research needs to be careful when taking students' self-reports on the "effortfulness" of a task as an indication of the object-level cognitive requirements of the task, as such appraisals may also reflect the affective-emotional requirements of task execution as well as motivational beliefs regarding the likelihood of success and meaningfulness of a task. A second conclusion is that instructional procedures rooted in cognition-oriented theory ideally are complemented by motivation theory to support student learning optimally.