Cost planning, as part of a cost management framework, is a total system that requires commitment from inception to the completion of a project. This chapter concentrates on the cost-planning activities, practices and techniques undertaken during the pre-tender design stages. It discusses the theoretical foundations for the activities involved in the cost planning process. An excellent description of cost planning is given by Seeley that summarises the aims of cost planning admirably: Cost planning aims at ascertaining costs before many of the decisions are made relating to the design of a building. The chapter provides details of the essential principles and framework to cost planning. The need for cost planning in building project activities is the same for any economic activity in a society. The chapter stresses the theoretical underpinning for understanding the nature and purpose of cost control activities. It identifies and describes the various stages in the RIBA Plan of Work.