This chapter provides a treatment of experimental design principles, focusing on their application in business experiments such as A/B testing, consumer behavior studies, and market research. It begins by defining key terms and explaining why randomization is the gold standard for establishing causal relationships. The chapter covers both classical and advanced designs, including completely randomized designs, factorial designs, and crossover trials. It also delves into the selection problem and the consequences of bias. Topics such as blocking, stratification, and factorial manipulation are discussed with an emphasis on practical implementation. Statistical notation is introduced to describe treatment allocation mechanisms, and visual diagrams help clarify complex ideas. Emerging research trends and limitations of traditional designs are also explored to prepare readers for real-world complexities.