Unwelcome surprises in the life of any organization can often be traced to the failure of an assumption that the organization's leadership didn't anticipate or had 'forgotten' it was making. Assumption-based planning (ABP) is a tool for identifying as many as possible of the assumptions underlying the plans of an organization and bringing those assumptions explicitly into the planning process. This book presents a variety of techniques for rooting out those vulnerable, crucial assumptions. The book also presents steps for monitoring all the vulnerable assumptions of a plan, for taking actions to control those vulnerable assumptions where possible, and for preparing the organization for the potential failure of those assumptions where control is not possible. The book provides a variety of examples and practical advice for those interested in carrying out an application of ABP in the fields of business, management, strategic planning, engineering, and in military applications.