With the rise of the Internet and the emergence of online shopping, traditional retailing has transformed substantially. Retailers have developed multichannel strategies and, in particular, have integrated their offline channels with online channels. Such an integration of offline and online channels is associated with the concept of cross-channel integration. This cumulative dissertation aims to investigate cross-channel integration holistically from a demand point of view and a supply point of view. It consists of four independent studies embedded in an overarching introduction and conclusion part. The first study provides the conceptual base by conducting a systematic literature review. It identifies, analyzes, structures, and extracts 169 publications in the research field of cross-channel integration and concludes by suggesting two dominant paths for future research. These two research directions are addressed in three subsequent empirical studies. One empirical study focuses on the consumer perspective by investigating channel switching behavior. It finds that customers have a fundamental need for certainty within and after the buying process when it comes to channel switching. The remaining two studies are related to the supply side of cross-channel integration and investigate effects of strategies, retailers can deploy when integrating channels. One study assesses the profitability of a channel addition. It establishes that adding an offline store to online channels increases profits absolutely, but reduces the profit margin in the short run. The other study related to the supply side conceptualizes cross-channel technologies along the customer’s purchase process and experimentally assesses one of these technologies. Finally, based on the insights of the four independent studies, the dissertation concludes by summarizing the contribution and by deriving overarching implications for researchers and practitioners, the latter are equipped with a checklist for cross-channel integration.