This book provides a conceptual systematization and a practical tool for the randomization of between-subjects and within-subjects experimental designs in social, behavioural, and health sciences. The author adopts a pedagogical strategy that allows the reader to implement all randomization methods by relying on the materials given in the appendices and using the common features included in any word processor software. In the companion website (www.fpce.uc.pt/niips/randmethods), along with other supplementary materials, the reader can freely download IBM SPSS and R versions of SCRAED, a package that performs simple and complex random assignment in experimental design, including the 18 randomization methods presented in Chapters 2 and 3.