Economic Appraisal and Cost Benefit Analysis (CBA) form the starting point in the development of an HVDC system. This section provides an overview of this complex process. The economic appraisal described here defines the studies to be undertaken to weigh the costs of an action against the benefits that it provides. In the context of transmission infrastructure development, the appraisal is carried out before the investment decision is taken, to support decision-making by estimating the effects of different options. The chapter is describing the CBA assuming that the initial assessment is to pursue an investment using HVDC transmission. That is, other alternative are assumed to be rejected in favor of HVDC solutions. However, the consideration of HVDC transmission systems in the planning process does not change the planning procedures currently employed by transmission network planners. It should also be recognized that not all HVDC transmission systems are planned by transmission planners. Many are now planned by developers of international interconnectors and remote generation developers (such as off-shore windfarms). The economic appraisal is described as a process comprised of discrete stages, beginning by defining the problem to be analysed and the need for investment, the identification of alternatives, assessing the costs and benefits, summarising results; and once costs and benefits have been confirmed the final investment decision made.