The terms ‘grandfather clause’ and ‘grandfathering’ describe elements of a policy program in which existing participants in an activity are protected from the impact of regulations, restrictions or charges applied to new entrants. In this paper, the role of grandfathering in the design of a carbon emissions trading scheme in Australia is assessed. It is argued that adjustment assistance policies such as those adopted in conjunction with previous microeconomic reform programs are preferable to policies based on the free issue of emissions permits.