This thesis research examines success factors for transactional eCommerce Websites focusing on technical and business contexts. Transactional websites in particular have become essential for eCommerce development and use. The researcher has adapted the three-phase process model from Delone and McLean’s I/S (Information system) success model (development, use and consequence), and conducted a comprehensive investigation to identify and determine success for transactional eCommerce website success. The primary research question: 1. What are the critical success factors for transactional e-Commerce websites? Sub Research Questions: 2. What issues essentially relate and encourage transactional eCommerce website success? 3. How do use and user satisfaction influence transactional eCommerce website success? 4. How can success factors for transactional eCommerce websites be categorized? 5. How can the success of transactional eCommerce websites be measured? In order to answer the above research questions, a mixed research method of survey and interview modes was applied to the research project. This research study has set its goal to identify, verify and categorize success factors for transactional eCommerce success, and to explore and discuss issues related to transactional eCommerce success. The researcher has identified 10 potential success factors (Site popularity, profit, performance and usability, security, design, content, transaction process and volume, shopping process, technical support and system development) for eCommerce websites from the secondary data (literature review and online tools). An empirical study was conducted to decide whether these factors are success factors for transactional eCommerce website, interviewing 8 eCommerce professionals and 52 end users. Primary data was collected from surveys and interviews to verify the hypotheses. Survey is a popular research technique generally with the quantitative approach recently. The sample size for the survey study was 52 in this thesis investigation. The researcher collected qualitative data by using interview as a technique, with 2 academic researchers in the field of eCommerce, 3 eCommerce website developers and 3 website owners. The findings and results indicate that the success factors which determine eCommerce development are usability and performance, security, technical support, web design, web content and system development process; also, site popularity and shopping process are factors related to the use of transaction eCommerce websites, while transaction process and volume and website profit are the factors of concern to business owners, and they belong to the eCommerce impact category. Furthermore, a theoretical model was proposed for further studies to examine the success of transactional eCommerce websites. The 10 success factors were categorized into three groups: transactional eCommerce development, use and consequences. The results also connect to three stakeholder groups of transactional eCommerce websites: developer, user and business owner.