This chapter provides a review of key developments in experimental design in barley breeding. After a brief history to set the scene, the chapter covers the background of experimental design for field trials, highlighting the key principles that are still fundamental for modern comparative experiments, including model-based design. The following section explores the quantification of genetic relationships through either pedigree or molecular marker information. Finally, the chapter presents the principles of multi-phase experiments for testing material both in the field and in the laboratory. Three case studies are included to highlight non-standard experimental designs that should be in the toolkit of every agricultural scientist and which are essential for modern plant breeding programs.