There is a heightened understanding that metacognition and strategy use are crucial to deep, long-lasting comprehension and learning, but their assessment is challenging. First, students' judgments of what their abilities and habits and measurements of their performance often do not match. Second, students tend to learn and comprehend differently depending on the subject matter, contexts, goals, and tasks. As a consequence, a student may appear to use deep, reflective strategies in one situation, and fail to do so in other circumstances. Third, it is generally assumed that strategy use (metacognition, metacomprehension) are separable constructs from the underlying skills germane to the target task. The studies described in this issue draw attention to the potential challenges to developing a pure (separable) measure of strategy use that is also reliable, valid, and contextualized.