This realist review aims to identify the working mechanisms and contextual preconditions for sedentary behavior (SB) change in older adults to guide the development of future interventions. The review followed the iterative process of Pawson et al. (1997). First, research questions were defined and an initial program theory (IPT) was established. Second, evidence was searched in four scientific databases and the grey literature. Third, data from 58 studies (explained in 61 papers) that contained relevant information to refine, refute or confirm the IPT were coded. And based on these codes, context-mechanism-outcome configurations were made and a final program theory was developed. As a result, three contexts for SB change became clear: (1) motivation, (2) opportunities, and (3) capabilities of older adults. Depending on the context, other behavior change techniques should be used to trigger specific mechanisms and reduce SB. Especially, the impact of automatic processes of SB on the effectiveness of SB interventions became clear. Currently, the focus is primarily on the reflective processes guiding SB, without taking into account that SB is often an automatic response which makes SB an ingrained habit. It can be concluded that the effectiveness of SB interventions in older adults highly depends on the intervention context.