From 2016 all new homes in the UK will be required, by law, to be 'zero carbon'. However, the detail of the Zero Carbon Homes standard is still being developed. Internationally there has been much debate on a definition for zero energy; though a consensus has yet to emerge. This paper presents an overview and synthesis of the literature on such definitions. Through a critical review, a series of options for the determination of a 'zero energy' or 'zero carbon' balance are revealed; the extent to which each option fully accounts for the energy consumed is also considered. The results demonstrate that a building which is zero energy or zero carbon should: account for regulated, unregulated and embodied primary energy; reduce its energy requirements as far as possible through fabric energy efficiency; and substantiate the zero balance through measurement of energy use as opposed to design stage predictions. The paper concludes that the current UK zero carbon concept is a misnomer and therefore should be amended in building energy policy.