The course covers the design of online experiments and analysis of A/B testing, and its role in measuring potential effect of various versions of a website or mobile application. The course also demonstrates the importance of user experience whether a new launch of product or website brings a substantial change through counterfactual analysis. Most of the technique could be applicable to advertising, financial reporting, marketing, product design, public relation, and social engagement in digital environment. The processes span from designing experiments with enough statistical power, characterising various metrics for evaluation, analysing the results and draw business insights, and ensuring the participants of the experiments are adequately protected.