While the taxation treatment of transactions under an emissions trading scheme (ETS) has the potential to support or distort the primary object of the ETS, taxation considerations are often overlooked in the process of designing a scheme. The approach taken in this regard in Australia and New Zealand (NZ) is worth noting because tax considerations played an integral role in the design process from the outset. This article provides an overview of the basic mechanics of the ETS designed by each of the Australian and NZ governments and a detailed analysis and critical comparison of the income tax treatment of emissions liabilities and units under the two schemes.