Discrete event systems ‎(‎DES‎)‎ have become pervasive in our daily lives‎.‎ Examples include ‎(‎but are not restricted to‎)‎ manufacturing and supply chains‎,‎ transportation‎,‎ healthcare‎,‎ call centers‎,‎ and financial engineering‎.‎ However‎,‎ due to their complexities that often involve millions or even billions of events with many variables and constraints‎,‎ modeling these stochastic simulations has long been a ‎"‎hard nut to crack‎"‎‎.‎ The advance in available computer technology‎,‎ especially of cluster and cloud computing‎,‎ has paved the way for the realization of a number of stochastic simulation optimization for complex discrete event systems‎.‎ This book will introduce two important techniques initially proposed and developed by Professor Y C Ho and his team‎;‎ namely perturbation analysis and ordinal optimization for stochastic simulation optimization‎,‎ and present the state‎-of‎-the‎-art technology‎,‎ and their future research directions‎.‎