How do plants, animals, and humans manage to survive and adapt to the urban environment? This book provides a comprehensive coverage of biological matters related to urban environments presenting both the conceptual and theoretical underpinnings, and practical examples required to understand and address the challenges presented by this novel environment. The Biology of Urban Environments focusses on urban denizens: species (both domesticated and non-domesticated) that live for all or part of their life cycle in towns and cities. The biology of household plants and companion animals is discussed alongside that of species that have become feral or have not been domesticated. Temporal and spatial distribution patterns are set out and generalizations are made while exceptions are also discussed. The various strategies used and the genotypic, phenotypic, and behavioural adaptions of plants and animals in the face of the challenges presented by urban environments are explained. The final two chapters contain a discussion of the impacts of urban environments on human biology and suggestions on how this understanding might be used to address the increasing human health burden associated with illnesses that are characteristic of urbanites in the early twenty-first century.