Background: Society is sitting more than ever before. Large-scale epidemiological evidence indicates that prolonged sitting time has negative health impacts including increased risk of metabolic syndrome, heart disease, weight gain, cancer, and premature mortality. Older adults are an important population to target because they represent the most sedentary segment of the population who struggle to meet activity guidelines. Based on these negative health associations, research on sedentary behavior interventions, especially focused on older adults, is a public health priority. Methods: This dissertation uses data from a pilot sedentary behavior intervention in 30 adults aged 50-70 years to understand how to measure and prompt sedentary behavior change. The intervention successfully targeted two distinct sitting interruption modalities (i.e., sit less, increase sit-to-stand transitions). Chapter 1 explored differences in self-reported and objectively measured sitting time to evaluate participants’ ability to self-assess behavior during an intervention. Chapter 2 included a mixed methods analysis of tool use to disrupt sitting time during the pilot intervention. Chapter 3 used focus groups to explore participants’ perceptions regarding wearable devices to track and change sedentary behavior. Results: Chapter 1 found significant differences in self-reported sitting time by day of week, employment status, and participation in a sedentary behavior intervention. Chapter 2 showed that participants who used effective tools were most successful in reducing sitting time. In contrast, current tools for increasing sit-to-stand transitions were ineffective. The focus groups from Chapter 3 revealed that participants were amenable to using wearable devices; however, current devices lack key features necessary for sedentary behavior including the ability to accurately measure sitting time and distinguish “inactivity” from standing. Discussion: Given the negative health outcomes associated with excessive sitting, more interventions are targeting sedentary behavior. The three themes explored in this dissertation (specificity of measurement, tools, and behaviors) and the combination of analysis methods help increase our understanding of sedentary behavior in older adults. This dissertation provides recommendations to improve the field by using specific measures for sitting time to capture differences across the week, designing interventions to include tools with a specific focus on sedentary behavior, and exploring how technology can help change behavior.