There have been calls for all housing to become ‘zero carbon’ in the future – that is, responsible for no carbon emissions through the use of fossil fuels, measured over a yearly basis – with the UK government in 2010 proposing a target date of 2050.The ultimate goal of zero-carbon developments and dwellings is attractive; but even for new dwellings it is expensive and relies on extensive use of renewable energy sources. All dwellings use energy for lighting, warm-up heating and appliances; depending upon the definition of zero carbon adopted (although this can be minimized by careful design and operation), the residual energy must be provided by zero-carbon sources such as biofuel, photovoltaics, hydropower, ocean power or wind, locally or nationally. For existing housing in existing areas, zero carbon will require resources and effort beyond what is currently available. This chapter looks at how the existing housing stock can move towards the concept of zero carbon, what options are available and what needs to be developed.