As the relative capital value of major real estate investment grows, and investment risk continues to centralise, the requirement to diversify this risk through shared ownership has increased. This international trend toward increased co-ownership has been manifested in cross border collaborations and, with this sharing of risks has come the dilemma of preserving the operational integrity of these assets and the capital value of the fractional interests created. This thesis considers the process of valuation of fractional interests, examining the methods employed in both the real estate and securities investment communities, and it identifies the shortcomings of the current unstructured approach to the problem. It reveals the impact of improperly structured agreements between co-owners on the value of their interests and illustrates the enormity of this in terms of the Australian publicly traded real estate securities sector. This thesis concludes that the current deficiencies in fractional interest valuation methodologies can be effectively addressed through the adoption, by professional real estate valuers, of a common approach to the investigation of the factors influencing the value of fractional interests and the terms of agreements which underlie these interests / Doctor of Philosophy (PhD)