Online dating applications have revolutionized the dating market in the past decade, but their exact effects remain unclear. We analyze the impact of the early diffusion of a popular dating app-Tinder-on college student dating behavior, relationships, and health. For identification, we rely on the ample qualitative evidence that Tinder's early promotion strategy focused primarily on Greek organizations on college campuses. Consistent with this evidence, we find that Tinder was more likely to be mentioned in college newspapers of universities with fraternities and sororities. Using a comprehensive survey with more than 1.3 million college student responses around the year of Tinder's rollout, we estimate a difference-in-differences equation comparing student outcomes before and after Tinder's rollout and across individuals and universities with varying Greek organization membership. We find that the rollout of Tinder led to a sharp and lasting increase in reported dating and sexual activity. At the same time, it led to an increase in reported unplanned pregnancies, STDs, and sexual assault. We observe no change in the number of reported relationship problems and, if anything, fraternity and sorority members experienced a relative decline in reported mental health issues. In terms of the distributional consequences, we find that the increase in sexual activity was mainly concentrated in Greek students and students who experienced a high baseline level of sexual activity.