This chapter is a tutorial on and review of a theory‐driven, quantitative approach to studying human information processing systems. Key properties in such systems comprise mental architecture, workload capacity, decisional stopping rules, and several varieties of independence, among others. We outline the early history of such interests, which began in the 19th century and then were reopened in the 1960s. We point out the hazards due to the frequent ability of even mathematically specified models to mimic each other's experimental predictions. Next, we show how the deepest properties of distinct psychological principles can, through what we term “meta‐theory,” be engaged to prove powerful theorems regarding model distinctions and transferred to incisive experimental designs that avoid the dilemma of model mimicry. This meta‐theory and its associated experimental designs have been implemented to address a wide variety of theoretical and empirical questions regarding attention, perception, psychophysics, memory processes, decision making, and categorization. This range of implementations—running from basic science to applied arenas such as clinical pathologies and human factors research—underscores the generality and potency of this approach.