What is stress, and how do we measure it? As stress research becomes increasingly inter- and transdisciplinary, it is crucial for researchers to have a common understanding of stress taxonomy, use precise terminology, and choose the most appropriate constructs and methods for their research questions. Together, these efforts will improve the quality, robustness, and reproducibility of scientific findings and allow the field to cohesively advance forward. This chapter briefly describes the history of stress research and offers precise language and definitions for commonly investigated components of stress. We then present the benefits and limitations of various methodological approaches that capture specific aspects of stressful experiences and stress responses, including methods of assessing exposure to stressful life events and chronic stressors retrospectively, the use of standardized in-lab stressors and naturalistic observations of stressful experiences (e.g., ecological momentary assessments), and methods for measuring stress responses, ranging from self-reported general stress perceptions to cognitive, emotional, behavioural, and physiological stress responses (i.e., neuroendocrine, cardiovascular, immune). To best integrate research findings, researchers are encouraged to consider the multiple and interconnected environmental contexts that impact individual differences in stressful life event(s) exposure and ability to adaptively cope with stress. The systematic and specific assessment of stress and its outcomes holds important implications for the advancement of the field, as well as the promotion of organizational and public policies in healthcare, the workplace, and schools. We include additional open access resources on stress measurement for further information.