This chapter focuses on between-subjects design, where separate groups experience different conditions. This method is ideal when exposure to multiple conditions is impractical or risks biasing responses. The chapter highlights random assignment as crucial for ensuring group comparability and controlling for confounding variables. Architectural examples, such as testing different facade designs with independent participant groups, demonstrate how between-subjects studies capture unbiased, first-impression reactions. Limitations, including the larger sample sizes required to detect effects, are addressed alongside strategies to mitigate them. This design is presented as essential when studying interventions that cannot be repeated within individuals.