According to the United Nations, 55 percent of the world’s population lives in urban areas, and this amount is expected to increase to 68 percent by 2050. The urbanization of the human population has come with significant environmental transformations. Since the pioneering works of William Cronon and Martin Melosi, in the 1990s, which called for historians to look at nature in the built environment, historians have responded to these transformations, giving rise to an urban subfield within the field of environmental history. Urban environmental history also draws from a long tradition in urban studies, which invites in-depth case studies, rooted in concrete experiences, while simultaneously taking a step back and considering large transnational trends in the urban experience, as in the works of Lewis Munford and Richard Sennet. This panel advances conversations emerging in this field, bringing together four scholars who examine urban environments on four different continents: North America, South America, Europe, and Asia. Isacar Bolaños studies how authorities in Ottoman Iraq tried to combat cholera and plague epidemics by improving urban sanitation from 1891 to 1914, before the establishment of the British Mandate of Iraq. Health and technology in cities are also important elements in Caitlin Murdock’s paper, in which she explores how concerns about exposures from x-rays, radium, and other forms of radiation drove debates about the use, regulation, and protection of spaces used as clinics, laboratories, and factories in the 1920s and early 1930s in Central Europe. In the American hemisphere, Kevan Malone examines the challenges of wastewater management in the international border area of San Diego and Tijuana in the 1960s and 1970s, highlighting the unequal balance of wealth and power during the rapid industrialization of the Mexican border city. Finally, Lise Sedrez discusses the scars of urban deindustrialization, a global process in the late 20th century, in the human and non-human populations of Guanabara Bay, Rio de Janeiro, Brazil. With its focus on four distinct world regions, this panel promotes comparative and transnational perspectives on the history of urban environments.