Book excerpt: Project estimating plays a vital role in project management. Typically completed in the initial planning stages, accurate project estimation can be a difficult task. Organizations and project managers should use these initial estimates to baseline the project schedule and cost, then refine these estimates as the project develops. Accurate estimation and refinement of the estimates leads to better and earlier decision making, thus maximizing value.Developed within the framework of A Guide to the Project Management Body of Knowledge (PMBOK&® Guide) &– Sixth Edition and other PMI standards, the Practice Standard for Project Estimating &– Second Edition focuses on providing models for the project management profession in both plan-driven and change-driven adaptive (agile) life cycles. This practice standard describes the aspects of project estimating that are recognized as good practice on most projects most of the time and that are widely recognized and consistently applied.PMI practice standards describe processes, activities, constraints, inputs, and outputs for specific discipline subject areas and are targeted to all practitioners within projectized organizations, not just project managers.