Written for a wide-range of mathematical abilities, this comprehensive, accessible overview emphasizes the conceptual aspects of decision-making rather than mathematical techniques or computer methods. Structured around a clear framework, the text first builds up the basic ideas of systems and shows how hard "OR" incorporates these concepts into its modeling process. It also incorporates important real-world aspects such as time, decision-making over time, constraints, uncertainty and multiple objectives into this framework, and shows how conflicts and ambiguities of world views lead to fundamental changes in the aims and models of decision-making approaches. A companion website is located at: http://www.palgrave.com/business/daellenbach/index.asp