This research studies the integration of customer relationship management -CRM-with modern data warehousing -DW- technology in the banking industry. The severe competition within the global financial service industry urges banks to upgrade their business intelligence systems, which ultimately increases their performance. Being the cutting-edge mass data solution, DW technology plays an increasingly important role in the customer segmentation process. In the context of such an environment, this study seeks to analyse the optimal implementation approach for integrating CRM with DW, using case study as the main research method. Five secondary cases and one primary case are studied. Secondary cases are selected with pre-determined criteria from the existing literature. The primary case is generated through an interview with one of the leading commercial banks in China. Based on the findings from both secondary and primary cases, the dissertation systematically reviews the critical issues of the implementation process. These critical factors are discussed in two main categories: external factors and internal factors. In addition, the customer segmentation process, which is the most important function of CRM, is analysed from both managerial and operational levels. DW infrastructures from different cases are compared and contrasted. This research contributes to both academic research and industry practice through the empirical findings and analysis. Further research on the conceptual and technological framework developed is also needed, as they are the important factors to the success of DW technology implementation.