This paper examines interface conditions between public and private spaces in residential back-laneways of Melbourne’s inner-suburbs that were characterized from extensive field observations and documentation. Specifically, it looks at the extent to which different interfaces enable or constrain everyday practices. The objective is first to analyse conditions of the built environment, and second to examine the potential for public reappropriation. In Melbourne, laneways are a common urban feature located predominantly in older inner-suburbs that have high population but low open-space densities. They were implemented in the 19th century for household sewage collection; but with improvements to urban infrastructure in the 20th century, their purpose became ambiguous. On a policy level, all laneways are currently classified as the smallest fragments of the overall road network. In practice, people reappropriate them in numerous other ways. What is at stake here is that these residential laneways could be the last remaining significant amount of underused inner-city land. In order to make visible the existing conditions, this paper surveyed a large area of inner-city Melbourne to capture the diversity and prevalence of different interface types on residential laneways. These interface types are further discussed in relation to observed laneway reappropriations. The paper concludes that more determined interfaces between public and private spaces offer less possibilities for public reappropriation, while undetermined conditions enable more public engagement.