The objective of the research, we would like to present, is to increase the transparency of investments into the existing housing stock in Germany for housing policy and other market participants. Regarding the existing stock the information about investment processes, market relevance, investors, housing conditions, renovations and modernizations from official data are inadequate. Therefore the aim of our project (financed by Ministry of Transport and Building) is to investigate investments into the German housing stock by: * Analyzing secondary data from different institutions (official and private) and * Collecting primary data by interviews. // Both approaches insure innovative results for the transparency of investments into the existing housing stock. The project consists of two parts: an analysis of secondary data and the collection and interpretation of primary data from interviews. a) The secondary data analysis is based on several statistical recourses. It deals for example with the amount and development of investments into the existing housing stock. Changes of the condition of residential buildings are identified form the point of view of inhabitants in order to estimate investment needs. Further more state initiatives for energy saving like interest reduced loans are discussed. Finally their macroeconomic importance for real estate investments within the existing stock is quantified. Financial supports of investments from government (such as interest reduced loans) and demographic developments are basic parameters for the profitability of investments in existing real estate premises. The profitability of these investments will be described taking into account empirical yield developments. b) Due to the fact, that market information especially about investments in the private rental market is missing, the collection of primary data focuses on this segment. More than 600 interviews in six German cities are conducted. The cities were selected in a manner that different market situations (different size; prospering, stagnating and shrinking; east and west) are reflected. Investment items, strategies, investment spending plans and the importance of public supports for private investors are basic topics of the primary data analysis. // Fundamental market information to support housing policies and to increase the transparency for market participants such as real estate lenders and investors. Indicators for a periodical investment monitoring are discussed. Approaches for segmentations of investments into the housing stock. In Germany investments into the housing stock exceed the investments for new construction since 2000. This is the case for West and East Germany with slight temporary differences. Nevertheless the number of flats constructed within existing housing stock remains quite low. Investments into the housing stock contribute to qualitative changes of the housing stock such as modernizations and energy savings. Especially in East Germany significant increases of the quality of housing stock took place as the improvement of the condition of buildings in the rental market indicate. At the same time investment needs in several housing segments (West Germany: construction period 1950/60; East-Germany: self user segment) become obvious. Looking at KfW-programmes for housing stock investments (interest reduced loans) the importance of purposes like heating/energy/insulation and modernizations will be discussed. The profitability of investments in existing real estate premises has a direct impact on investment decisions. As it will be shown the average total return from stock investments in the residential market of Germany is moderate but less volatile than of other capital investment items. However negative capital growth rates are an investment hindrance.