Interpersonal synchrony usually means that people mutually adapt their behavior to each other over time. Such behavioral adaptivity is assumed to be driven by some form of subjective internal synchrony detection. In contrast to objective synchrony detection by an external (third-party) observer, subjective synchrony detection relies solely on information that is perceived by each of the synchronizing persons. Simultaneous actions of the two persons in principle cannot be sensed instantaneously by one of the two persons, but will involve time lags. These time lags reflect the time differences between the pathways for a person’s sensing of the own actions and for the sensing of the actions of the other person. In the computational agent model described in this chapter, we explore the role of time lags in different types of subjective synchrony detection and its involvement in behavioral adaptivity. Multiple simulation experiments show expected types of patterns of subjective time-lagged synchrony detection and related behavioral adaptivity.