This lecture discusses the evolution of online dating as a significant aspect of modern social life, transforming from a stigmatized practice to a common activity. The instructor presents a twofold approach to studying online dating: first, as a research topic that reveals contemporary sexual norms and behaviors, and second, as an observation site that provides valuable data for sociological inquiry. The presentation highlights the use of big data from dating platforms to analyze partner preferences and matching mechanisms, offering new insights into couple formation. The instructor shares findings from various studies, including the dynamics of social homogamy and the age gap between partners, emphasizing the importance of understanding user behavior through empirical data rather than relying solely on survey responses. Limitations of online dating data are also addressed, including issues of representativeness and the accuracy of user profiles. The lecture concludes by underscoring the potential of online dating data to enhance sociological research and provide a deeper understanding of partner choice.