We study the adoption of Common Application membership by private four-year postsecondary institutions and its role in explaining the growth in undergraduate applications. Using data from the College Board’s Annual Survey of Colleges, proportional hazards models suggest that institutions respond to the net benefit of adoption. We then estimate that membership increases applications by 5.7–7.0 percent and decreases yield rates by 2.8–3.9 percent. Acceptance rates decrease for members when their local networks are large. Falsification tests indicate that membership effects occur as a one-time adoption shock. Membership also decreases SAT scores and increases the percent students of color.