This chapter clarifies the fundamental concept of experimentation as the deliberate manipulation of independent variables to observe their effect on dependent variables. It contrasts experiments with quasi-experimental and observational methods, underlining the strength of experiments in identifying causal mechanisms. The chapter explores the iterative nature of experimentation, showing how repeated testing and refinement lead to stronger, user-centered designs. Practical examples illustrate how experimental methods can reduce uncertainty, accelerate learning, and secure stakeholder confidence by producing verifiable results before construction. Readers gain a foundational understanding of how experiments transform architectural research from descriptive to explanatory, making findings more actionable and generalizable.