A broadening research program focused on environment and security emerged over the past 30 years. But the meaning and operationalization of environment and security have been an implicit and increasingly explicit part of the scholarly debate. Approaches range from the more specific focus on the linkages between environmental change and violent (deadly) conflict, the possible role of environmental conservation, cooperation, and collaboration in promoting peace, and the broader focus on potential relationships between environmental change and human security (understood as freedom from both violent conflict and physical want). In addition to the different conceptions of environment and security, the type and direction of causal relationships among different factors continue to be a focus of research. With respect to the environment and violent conflict, which constitute the largest explicit research stream on environment and security, the debate has centered on whether and why environmental scarcity, abundance, or dependence might cause militarized conflict. Less research has been conducted on the environmental effects of violent conflict and war or traditional security institutions such as militaries and military-industrial complexes. Rigorous research on the consequences of peace or human security for the environment is virtually nonexistent.