Several dilemmas and paradoxes are encountered in the present way of managing the urban green in Rotterdam. There is quite a discrepancy between the extensive political attention given to green areas outside the city’s limits and the rather limited attention to the urban green itself. Although the quantity of urban green is quite large when expressed in square metres, its quality is rather poor. The way it is used can also be improved. The management of the urban green poses another dilemma. ‘Naturally’ maintained green areas have a higher ecological value, but they have a lower potential for use and often look untidy in the eyes of the citizens. Choices have to be made, and here a distinction into ‘layers’ can be used in order to formulate the ambitions. These ‘layers’ are (1) the compact urban area, (2) the post-war extension areas, (3) the network of parks and woods, (4) the port, the river, and the dunes, and (5) the agricultural landscape. Especially the parks and forests, the agricultural areas, and the water ‘network’ are the nucleus of the municipal Nature Policy. Much knowledge is, h o w e v e r, lacking. This is partly caused by the spread of knowledge over a great many persons and institutions (societies). Rotterdam, therefore, looks with envy at cities like Berlin and Leipzig, where such knowledge is concentrated. In Rotterdam too, biotope mapping is to be started. It is then a question how the results of the mapping can be used as an instrument in the dynamic practice of urban planning. Preferably the mapping provides results and information that can be implemented in the urban planning process.