Previous research has shown the negative impact of sedentary behavior on health, including cardiovascular risk factors, chronic disease-related morbidity, and mortality. Accurate measurement of sedentary behavior is thus important to plan effective interventions and to inform public health messages. This article (a) provides an overview of the nature and importance of sedentary behavior, (b) describes measurement methods, including subjective and objective measurement tools, (c) reviews the most important measurement and data processing issues and challenges facing sedentary behavior researchers, and (d) presents key findings from the most recent sedentary behavior measurement-related research. Both subjective and objective measures of sedentary behavior have limitations for obtaining accurate sedentary behavior measurements compliant with the current definitions of sedentary behavior, especially when investigating sedentary behavior as part of the full spectrum of physical behaviors. Regardless of the sedentary behavior measure chosen, researchers must be aware of all possible sources of error inherent to each technique and minimize those errors, thereby increasing validity of the outcome data.