The high demand in science and engineering communities requires more efficient and intelligent solutions to complex optimization problems dealing with a wide variety of real-world problems. This book introduces an effective method of optimization known as extremal optimization (EO). In research monograph and tutorial fashion, the book brings together the fundamentals, techniques, and algorithms of EO. It covers modified EO and multi-objective EO along with many numerical and benchmark examples based on original contributions and the authors' recent research results.