The effects of the surge in second-home buying (homeowners acquiring nonprimary residences) on the housing boom and bust remain an open question partly because reliable geographic data is currently unavailable. This paper constructs local data on second-home buying by merging credit bureau data with mortgage servicing records. The identification strategy exploits the fact that the vacation share of housing in 2000 predicts second-home origination shares during the boom years, while also uncorrelated with other boom-bust drivers including proxies for local housing expectations, the use of alternative and privately securitized mortgages, and supply constraints. Areas with plausibly exogenous increases in second-home buying experienced a sharper boom and bust. Overall, second-home buying could explain about 30 percent and 10 percent of the run-up in construction employment and house prices, respectively, from 2000 to 2006.JEL codes: R12, R21, R31