Research methods are the cornerstone of I-O psychology. This chapter addresses the relationship between research and theory; basic research concepts and the research designs and methods commonly used in I-O research; the uses of common statistics used to analyze data; the ways for estimating the reliability of a psychological measure; the typical ways to operationalize measurement validity; some of the core ethical issues faced by I-O psychologists in their research; key legal and global issues around research in organizations; and the current issues and research around research methods.