The functional-cognitive framework for psychological research implies that functional and cognitive researchers operate at two separate but mutually supportive levels of explanation.From a functional-cognitive perspective, all applied psychologists are ultimately directed at the functional level but they can differ in the way they conduct functional research and the degree to which they seek guidance from cognitive models. We propose a taxonomy that encompasses four different types of applied psychology and evaluate the merits of each type.We also argue that applied psychology can be fortified by strengthening its functional core, thus evolving into a more integrated but still diverse discipline of psychological engineering.Finally, we explore the implications of these ideas for applied memory research.Keywords: functional psychology, cognitive psychology, levels of explanation In a recent paper, Hughes, De Houwer, and Perugini (2016) likened the current state of psychological science to an archipelago of islands, each home to a different "tribe" of researchers. The members of the various tribes differ not only with regard to the topics that they study (e.g., psychopathology, social behavior, …) but also with regard to the approach that they adopt when studying these topics. Generally speaking, communication between the different islands is limited. This is particularly the case for two groups of islands, one group that adopts a cognitive approach and a second group that adopts a functional approach. The cognitive approach has dominated psychology for about half a century now. It aims to uncover mental mechanisms, that is, the way in which organisms process information (see Bechtel, 2008;Gardner, 1987). The functional approach, on the other hand, can be linked to behaviorism, at least certain forms of behaviorism such as radical behaviorism as it was introduced by B. F. Skinner (see Chiesa, 1992Chiesa, , 1994Hayes & Brownstein, 1986) and to more recent scientific approaches such as contextual behavioral science (Hayes, BarnesHolmes, & Wilson, 2012). Functional psychologists, as we will call them, are interested primarily in the environmental determinants of behavior, that is, in the way that behavior is a function of the (present and past) environment. 1 The cognitive approach is often thought of as a reaction against and thus as incompatible with the functional approach. For instance, in a column about the state of behaviorism at the centenary of B. F. Skinner's birth, Roediger (2004) cited Tulving who argued that "psychology now designates at least two rather different sciences, one of behavior 1 We use the term "functional" in the mathematical sense of "function of" (i.e., behavior is a function of the environment) rather than in the teleological sense of "function for" (i.e., behavior serves a purpose). This also clarifies the distinction between functional psychology as we see it (i.e., the study of environment-behavior relations) and functional psychology as the approach adopted by a group of A...