This article proposes a population ecology perspective on organization-environment relations as an alternative to the dominant adaptation perspective. The strength of inertial pressures on organizational structure suggests the application of models that depend on competition and selection in populations of organizations. Several such models are discussed, along with issues that arise in applying them to the organization-environment problem. The authors argue that the adaptation perspective, which focuses on subunits of organizations making strategic responses to environmental opportunities and threats, has been overemphasized in organizational theory and research. They propose a population ecology approach that emphasizes the role of selection and competition in shaping organizational structures. The article explores the challenges of applying ecological models to human organizations, including the transmission of non-genetic information and the expansion of organizations. It also discusses the principle of isomorphism, which posits that organizations in equilibrium are specialized to highlight environmental characteristics, and the theory of niches, which suggests that organizations should be generalists in unstable and uncertain environments. The authors conclude by highlighting the need to balance adaptation and selection processes in understanding organizational diversity and change.This article proposes a population ecology perspective on organization-environment relations as an alternative to the dominant adaptation perspective. The strength of inertial pressures on organizational structure suggests the application of models that depend on competition and selection in populations of organizations. Several such models are discussed, along with issues that arise in applying them to the organization-environment problem. The authors argue that the adaptation perspective, which focuses on subunits of organizations making strategic responses to environmental opportunities and threats, has been overemphasized in organizational theory and research. They propose a population ecology approach that emphasizes the role of selection and competition in shaping organizational structures. The article explores the challenges of applying ecological models to human organizations, including the transmission of non-genetic information and the expansion of organizations. It also discusses the principle of isomorphism, which posits that organizations in equilibrium are specialized to highlight environmental characteristics, and the theory of niches, which suggests that organizations should be generalists in unstable and uncertain environments. The authors conclude by highlighting the need to balance adaptation and selection processes in understanding organizational diversity and change.