All public investment projects in Ireland with a capital value in excess of €20 million are required to be subject to appraisal in the form of either Cost Benefit Analysis (CBA) or Cost Effectiveness Analysis (CEA). The practice and application of policy appraisal has undergone significant change globally, driven in large part by sustainability and climate change considerations. This paper examines key practice issues including discount rates, time horizon, the range of costs and benefits to be appraised and carbon pricing. The paper is mainly concerned with how changes within CBA can make it more appropriate to the context of climate change and transition. However, it also examines the way in which key characteristics of climate transition challenge conventional approaches to CBA and points to the need to explore other analytical and strategic approaches to transition.