The related issues of vacancy, redundancy and dereliction in the city, raise questions about the conflict between private profit and social use, between exchange values and use values. This paper offers a typology of the causes and forms of vacancy and is the first attempt to map this phenomenon for nineteenth-century Dublin. It also reviews some of the contemporary debates about the management of empty and decrepit buildings and sites. The charge of wastefulness was weighty and suggested strategies that are relevant yet today. These include compulsory purchase, a tax on emptiness, informal occupation, and the temporary appropriation of un-used spaces for socially-useful purposes.