This project introduces the cost variable inside the critical chain methodology at project management. To achieve this goal, it is developed a bibliographical survey, followed by the definition and classification of two types of costs: Static and Dynamic. After that, two new definitions are made: cost critical chain, which is the sequence of activities with higher dynamic costs; and cost buffer, that garanties the security of the project with the consideration of the uncertainties of the cost of the activities. Finally, it is shown how to use this proposal, through the explaning of the planning and control of the project in this new context