The e-Retail industry has grown rapidly over the last few years and is projected to continue its upward trend as consumers shift from traditional channels to online channels. In March 2010, Forrester Research forecasted that online retail sales will grow by 10% a year for the next 5 years and e-Retail sales will amount to $249 billion by 2014. With intense competition for market share and profits, information systems and technology (IST) sourcing decisions are becoming increasingly important to e-Retail firms to support continued growth and market responsiveness. There are several aspects for e-Retailers to consider when formulating its IST sourcing strategy. Whether to choose make versus buy for technology assets and services has been addressed in both strategy and IS literature (Handfield et al. 1999, Leiblein et al. 2002, Wade and Hulland, 2004). Then there is the follow-up question of selecting a best-of-breed strategy or tighter partnership with a select group of vendors (Clemons et al. 1993, Kauffman and Tsai 2009). Few studies have looked at IST sourcing or proposed models and frameworks for evaluating IST sourcing decisions (Saarinen and Vepsalainen, 1994). Furthermore, these existing studies mainly address the antecedents of the decisions but not so much on their performance effects (Kauffman and Tsai 2009; Smith et al., 1998). The goal of this study is to extend the knowledge of IST sourcing for e-Retailers, a topic which has received limited attention (Kishore et al., 2004), by addressing a core problem: How should an e-Retailer develop and implement its IST sourcing strategy to accommodate the increase in consumer demand and IT complexity but still achieve high performance? The study introduces two theoretical models to examine organizational factors that influence an e-Retailer's IST sourcing strategies of make versus buy and partnership versus best-of-breed. The proposed models are tested using a panel data set of 307 e-Retail firms over the period of 2006 to 2010. The study opens up the black box of internal firm operations by introducing a granular view of IST sourcing decisions at both the value chain and e-Commerce architecture levels and examining the performance impacts of these strategic choices. This in-depth look at IST sourcing has yet to be explored in the literature.