Analyzes psychological research to offer insights into how methodological and ontological questions are intertwined.   Psychology has seen an intense debate about the lack of replicability of results in recent years. Uljana Feest uses history and philosophy of science to shed light on the nature of experiment in psychology in general, but her aim reaches beyond debates about replication to provide a novel and comprehensive analysis of the investigative process in experimental psychology. She shows that the central unit of analysis for our epistemological considerations of psychological research should be not theories but, rather, concepts. Her guiding question is: How do psychological concepts figure in the experimental exploration of the objects of psychological research? For Feest, this question has two intertwined aspects: What role do concepts play in the design of experiments and the production of data, and how can concepts be revised or adapted in response to experimental results. Following the historical trajectory of debates about operationism in psychology, she argues that this debate was not concerned with philosophical theories of meaning but, instead, closely connected to the investigative practices of experimental psychologists. The book offers a broad analytical framework for thinking philosophically about the investigative process in psychology, including analyses of the relationship between data and phenomena in psychology, the relationship between folk- and scientific psychological concepts, the relationship between genuine results and experimental artifacts, and the nature and exploration of psychological kinds.