Prolonged sitting is increasingly being considered a severe concern in public health recommendations, which suggests that all adults should reduce the amount of daily sedentary time. This review examines several crucial aspects of sedentary behaviors and health and discusses the possibilities of developing public health guidelines on daily sedentary time. The following issues were observed and analyzed to review the evidence regarding sedentary time and health: First, the profile of the daily sedentary time of adults across different countries was described. Second, the physical activity guidelines provided by the World Health Organization or government authorities of various countries were reviewed. Third, evidence was obtained on systematic reviews and meta-analyses to explore the recommended limit of daily sedentary time; spending a higher amount of time on sedentary activities than the recommended threshold may damage adult health. Fourth, measurement methods of sedentary behaviors may moderate the associations between sedentary time and mortality across studies. Finally, conclusions and suggestions for future research were proposed. In summary, an increased sedentary time is associated with high morbidity and mortality risks in adults. Self-reported questionnaires typically underestimate the total sedentary time compared with that obtained using device-based measures. Recent metaanalyses revealed that sedentary time of >9 h/day may increase the all-cause mortality risk. However, based on few studies conducted with objectively-assessed sedentary time, the current evidence is insufficient to form guidelines. More large-scale and long-term prospective studies with objective measures of sedentary time are required to validate these findings.