In the retail sector, consumers typically patronize multiple outlets for a variety of products, which raises the important issue of how outlets can gain a greater share of consumer expenditures. One such way is to increase repeat purchases through loyalty programs. This article examines the impact of loyalty programs, which target existing customers, on repurchase behavior in grocery stores. It finds that heavier, more frequent customers of a store enroll in the loyalty program earlier; that buying behavior changes only slightly after buyers join the program; and that small changes in loyalty appear to erode 6-9 months after buyers join.