The study of nonhuman animals in urban ecosystems is a recent but expanding field. This chapter explores the ways in which human-animal relationships in cities have historically been framed and argues that a consideration of nonhuman animals is vital to a robust urban theory in the age of ecology. The places of animals within the urban planning and design professions that shape cities are elucidated, along with contemporary developments in ecology that increasingly inform city planning, design, and management. The chapter then highlights four global dynamics that promise to radically reshape urban animal ecologies, and concludes with a call for lively cities characterized by the coexistence of people and animals.