As real estate has matured as an asset class it has become increasingly ìglobalî, with fund management platforms and investment mandates being developed across global markets. Despite this globalisation of the asset class, there remain significant differences in the estimates of the size of the global market, ranging from $3 to $30 trillion. These differences have important potential implications for real estate. On the one hand, they raise questions over appropriate allocations to the asset class, particularly if these allocations are based on the size of the market relative to equities, bonds and other alternatives. On the other, different estimates of individual market sizes can influence strategic allocations across those markets. It is within this context that this paper investigates different methodologies for estimating market size, comparing definitions and results for the different approaches. Given the variations in data quality, the paper distinguishes between ìmatureî and ìdevelopingî real estate markets, explaining the methodologies for each. The paper takes forward the analysis carried out in a paper presented at ERES in 2011 focused on the Dutch market (Teuben, B and Courtens, R. (2011) The real size of the Dutch real estate investment market; Working paper ERES Conference Eindhoven). It is likely that the paper will represent an important step towards more authoritative estimates of global market size.