This book explains the basic technique of the genetic algorithm and shows how design engineers can use a genetic algorithm to solve real design engineering problems. This paper focuses on explaining how genetic algorithms work. A brief example at the end demonstrates how the practicing engineer can use this powerful technique to solve real world problems in engineering design. The example of a helical compression spring design problem uses a genetic algorithm to minimize the weight of a spring, but the genetic algorithm can be applied to almost any type of design problem.