Product unavailability is a frequently occurring and universal issue, and a major concern for retailers and manufacturers alike. In this chapter, the authors focus on product unavailability within a consumer packaged goods context, taking the perspective of the retailer. They distinguish between four types of unavailability based on their timing (temporary versus permanent) and scope (narrow versus broad): out-of-stocks, permanent assortment reductions, brand delistings and conflict delistings. These four product unavailability types significantly differ not only in their nature and underlying causes, but also in the (prevalence of) response options available to consumers, and the ensuing sales losses for the retailer. Building on extant literature, the authors discuss the factors that moderate the sales implications of different unavailability types, and the managerial actions that may mitigate their negative impact. Finally, the authors also highlight several substantive and methodological issues that remain currently unaddressed and constitute a fruitful future research agenda.