Many retailers believe that a majority of purchases are unplanned, so they spend heavily on in-store marketing to stimulate these types of purchases. At the same time, the effects of “preshopping” factors—the shoppers' overall trip goals, store-specific shopping objectives, and prior marketing exposures—are largely unexplored. The authors focus on these out-of-store drivers and, unlike prior research, use panel data to “hold the shopper constant” while estimating unbiased trip-level effects. Thus, they uncover opportunities for retailers to generate more unplanned buying from existing shoppers. The authors find that the amount of unplanned buying increases monotonically with the abstractness of the overall shopping trip goal that is established before the shopper enters the store. Store-linked goals also affect unplanned buying; unplanned buying is higher on trips in which the shopper chooses the store for favorable pricing and lower on trips in which the shopper chooses the store as part of a multistore shopping trip. Although out-of-store marketing has no direct effect, it reinforces the lift in unplanned buying from shoppers who use marketing materials inside the store. The authors discuss the implications for retailers.