This chapter considers two media of transport - road and air - and how the fiscal-transport interface impacts on the environment. These are chosen as being the areas of most concern in environmental terms, although the main focus is on road transport, which is the area most affected by the fiscal structure and through which most transport takes place. The chapter discusses the environmental and other external impacts of transport. It examines the existing transport fiscal structure, and the environmental effects thereof, and asks the question - do transport users pay the full costs of transport that is to what degree is the external costs internalised. The chapter explores the options that exist for adjusting the fiscal structure to internalise the externalities and make it more environmentally 'friendly’ and also discusses a possible approach for future policy. In a number of ways the Irish fiscal treatment of transport is quite environmentally positive.