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". Assumption-based planning (ABP) is a tool for identifying as many as possible assumptions underlying the plans of an organization and bringing them explicitly into the planning process. This book presents a variety of techniques for rooting out those vulnerable, crucial assumptions. It also presents steps for monitoring the vulnerable assumptions of a plan by taking actions to control them where possible and preparing for potential failure where control is not possible.