In the authors’ view, the existing urban planning system is not favourable to the temporality and variability of urban wastelands, which complement traditional urban greenery through a range of functions such as; gardens, meeting spaces, places to walk the dog etc. Consequently, the aim of the paper is to investigate functions and possible scenarios for the development of urban wastelands in Poland. The methods used in the research include a comparative assessment of wasteland case studies from Warsaw and Tarnów and a comparison of possible development scenarios based on case studies from different cities across Europe. Wastelands were researched to establish their location, their functions, the distance from inhabited areas and the types of other green areas located within a 5 min. isochrone from the surrounding housing area. Case studies of development scenarios were researched to establish their changing functions, the continuity of design and the algorithm of creation. The authors conducted qualitative interviews, mapping, inventories of territorial marks (makeshift benches or other constructions made by users showing the way they ‘own’ the area), investigation of local development plans and literature reviews to gather the data used. The collation of results has led to the creation of a ‘wastelands toolkit’ – a tool dedicated to urban planners and decision makers.