This thesis provides a theoretical framework for evaluating the causes of vacant land in shrinking cities. The focus of this thesis was New Orleans and St. Louis; these two cities were selected as the case studies because they are roughly of similar age, possess a common cultural and economic heritage, and have a geographic footprint which encompasses different environmental conditions. This thesis evaluated factors that contribute to patterns of land vacancy within these two cities. Factors included in this evaluation include employment and other economic and cultural opportunities, environmental and ecological conditions, social dynamics and conditions, governmental management decisions, and 'quality of life' stressors, such as proximity to major infrastructure and industrial development. The theoretical framework described in this thesis is intended to apply to other shrinking cities beyond the case studies. A geographic information system database using historical maps and population census data were created for each city and utilized to examine temporal patterns in the relationship between land vacancy and a variety of environmental, economic, and social factors. Maps from the time of the founding of each city were geo-referenced to create a depiction of the ecological conditions prior to European settlement at the sites of New Orleans in 1718 and St. Louis in 1764, respectively. Time-series data gathered from the United States population censuses were utilized to document spatial change of the two cities as they evolved. Homo sapiens like other species compete for habitat. Access to high quality habitat within the urban ecosystem is determined by contestation between individuals and social groups, through market mechanisms and through management decisions, both utilitarian and ideological. Corruption and violence may also be factors. Individual agency is a factor in this contestation but social and cultural structures can also work to limit individual choices, particularly for minorities and low income residents, and relegate many residents to suboptimum or marginal habitat. A data analysis of both New Orleans and St. Louis showed that the quantity and location of vacant land is primarily influenced by proximity to opportunities and by proximity to major risks which impact the quality of Homo sapiens habitat. The first of these is proximity to opportunities such as employment, education, and cultural resources. The second is the presence of natural hazards, such as flooding and geological hazards, as revealed by the analysis of the historical ecology of the city. The third is the impact of local government management decisions and social planning which has spatial implications, including racially-based zoning, racial covenants, redlining, and isolation from public services and facilities such as the segregation of public schools. These decisions are often the reflection of ideology and power relationships. A fourth driver of land vacancy is proximity to risks, notably industrial lands, but also the intrusion of major infrastructure projects such as the development of the railyards and rail corridor of St. Louis, the construction of the Industrial Canal in New Orleans, and the construction of Interstate highways through both cities. In some circumstances, such drivers that include the unintended consequences of utilitarian decisions. The fifth driver include socio-economic factors and the neighborhood effects of crime, and poor education. These five drivers act in different proportions in each city to influence land values which, in turn, drive levels of vacancy. This comparative investigation revealed that the impact of geophysical factors on land vacancy varies greatly between New Orleans and St. Louis. While much of New Orleans lies below sea level and is often subject to flooding and hurricanes, little of the vacant lands of St. Louis are impacted by geophysical factors. In contrast, management decisions and social planning have contributed significantly to the concentration of poverty and, in turn, land vacancy in both cities. While some of these management decisions are utilitarian in nature and intended to provide the greatest benefits for the most number of people, others are ideologically driven or reflect power relationships and in the case of both New Orleans and St. Louis, racism. Proximity to risks, such as active railroad tracks, major highways, and industrial development, also has a strong relationship to land vacancy in both cities. Land vacancy also has a strong spatial relationship with areas of low income, poor education, and crime and neighborhood effects. While an understanding of environmental history can provide a useful guide to vacant land policy, efforts to address the challenge of vacant lands must consider not only the symptoms but the underlying causes of vacancy, particularly economic and social factors. This thesis is addressed to planners, architects, urban designers, landscape architects, and elected and appointed government officials who work to address the challenges of shrinking cities. Though this thesis examined the causes of vacant land in two shrinking cities, future research should examine the application of the theoretical framework presented here to cities experiencing growth as well.