As enunciated by Ronald A. Fisher, a randomized block design (RBD) is the simplest design for comparative experiment using all three basic principles of experimental designs: randomization, replication, and local control. In this design, the treatments are allocated to the experimental units or plots in a random manner within homogeneous blocks or replications. It is appropriate only when the experimental material is heterogeneous. It may be used in single- or multifactor experiments. This entry considers the application, advantages and disadvantages, layout, randomization methods, and statistical analysis of randomized block designs.