In our interpersonal relationships, conflict is inevitable—and a cause for concern. Although prior literature has examined physiological and behavioral indicators of interpersonal conflict, research has yet to identify its neural underpinnings. Measuring dynamic patterns of brain activity within interpersonal interactions like conflict has become possible thanks to the advent of “hyperscanning.” By capturing simultaneous brain activity in real-time (i.e., inter-brain synchrony), hyperscanning can reveal the extent to which people are engaging cognitive processes (e.g. mentalizing) similarly. In the current study, we used functional near-infrared spectroscopy (fNIRS) to measure inter-brain synchrony within romantic couples engaged in face-to-face conversations characterized by conflict and affiliation. Inter-brain synchrony was recorded within regions of the mentalizing network—the medial prefrontal cortex (mPFC) and temporoparietal junction (TPJ)—and will be compared across conversation type. With our findings, we aim to establish baseline neural synchrony measures for different complex interpersonal interactions.