To what extent should multichannel retailers integrate assortments across channels? Previous literature controversially discusses the question of which integration strategy is most successful but arguments are only conceptual, and no empirical assessment exists. This article presents a framework that (a) shows how customers' perceived shopping benefits of variety, convenience, and reduced risk mediate the impact of multichannel assortment integration (full, asymmetrical, no) on patronage intentions and (b) differentiates the impact for retailer types based on substitutive, complementary, and independent assortment relations. Two large-scale experimental studies empirically investigate whether a dominant integration strategy exists in the context of full and simultaneous information (Study 1) and more uncertain and subsequent information accessibility (Study 2). We consistently find that full integration dominates no integration across assortment relations, but asymmetrical integration-the strategy that is most often realized by multichannel retailers-can have a detrimental impact for substitutive relations compared with no integration. Asymmetrical integration can be more beneficial than full integration for independent relations, while customer outcomes differ less for complementary relations. Researchers and managers can use our findings to understand how shopping benefits of variety, convenience, and reduced risk explain the different customer outcomes of multichannel assortment integration, depending on retailer type.