This document explores the fundamental concepts of project cost management, encompassing various estimation techniques, the development of a comprehensive cost management plan, and the analysis of budget performance. It delves into the application of earned value management (EVM) and the To-Complete Performance Index (TCPI) to assess cost variations. Furthermore, it examines the process of replanning to bring a project back on budget, including the identification of issues and recommendations for improvement. The document concludes with a review of cost management performance and lessons learned.