Online platforms have emerged as a dominant business model in numerous industries in the new millennium. In light of the substantial and burgeoning body of empirical platform research, this article synthesizes extant studies and identifies the evolution of underlying research methodologies and topics. Building upon a database of 860 empirical online platform papers in premier journals during the first two decades of the new millennium, this article presents a categorization framework based on the online platform type (including search platforms, e-commerce platforms, online communities, and mobile platforms) and research perspective (including platform participants, platform orchestrators, and platform ecosystems). We provide a critical review of noteworthy trends and highlight directions for future research in each category of the proposed framework. A comprehensive bibliometric analysis is then conducted to visualize and track scholarship in empirical online platform research. Lastly, we adopt an interdisciplinary lens to synthesize our critical review of empirical online platform research into lessons and research opportunities that emerge from multiple disciplines.