MCDA, or multi-criteria decision analysis, is the set of tools and methods we explore in this book. MCDA provides mathematical methodology that incorporates the values of decision makers and stakeholders as well as technical information to select the best solution for the problems that they may face; it allows for a more logical and scientifically defensible decision to be made. This chapter discusses the need for formalization of the decision process and explores the types of methods and their relative strengths and weaknesses. It also introduces software called DECERNS, which can be used in conjunction with this book to explore the use of different MCDA methods and applications.