Organ-on-a-chip technology is ideally suited to cultivate and analyze 2D/3D cell cultures, organoids, and other tissue analogues in vitro, because these microphysiological systems have been shown to generate architectures, structural organization, and functions that closely resemble their respective human tissues and organs. Although great efforts have been undertaken to demonstrate organotypic cell behavior, proper cell-to-cell communication, and tissue interactions in recent years, the integration of biosensing strategies into organ-on-a-chip platforms is still in its infancy. While a multitude of micro-, nano-, and biosensors are well established and could be easily adapted for organ-on-a-chip models, to date only a handful of analytical approaches (aside from microscopical techniques) have been combined with organ-on-a-chip technology. This chapter aims to summarize current efforts and survey the progress that has been made in integrating analytical techniques that are being implemented for organ-, multi-organ-, and body-on-a-chip systems based on electrochemical and optical sensors.