Since the path-breaking work of prominent North American historians such as Joel Tarr and Martin Melosi, as well as more recent roundtables in Europe, urban environmental history is now a mature research field, at the intersection of various related approaches. Time has passed since a leader of environmental history, William Cronon, could write that ‘cities in particular deserve much more work than they have received’. In this field, urban history necessarily crosses with environmental history, but also with the history of technology and social and cultural history; whilst its scholars not only emanate from a traditional historical background, but also from geography, science and engineering. Urban environmental historians, as they are referred to here, have duly established the importance of studying the relationships between ‘nature’ (including non-humans) and humans in and around cities. This ‘nature’ is a complex and shifting entity: recent doctoral studies have, for instance, documented rivers transformed by human action, weeds growing in the spatial and social margins of cities and tidal wetlands progressively filled in and built upon. The recently completed Ph.D.s reviewed in this essay see the built environment more as a hybrid of natural elements, like water, plants, animals and human action. Aided by the environmental lens, the scope of the urban historian has also been broadened by studying the ways in which residents’ lives were transformed by the invention, spread and environmental impact of new technologies, as well as the political responses to environmental crises.