Nobel laureate Wassily Leontief introduced input-output (I-O) models in the 1930s as a decision-making tool, providing a comprehensive understanding of economic processes such as production, income generation and consumption. These models go beyond economic applications and are valuable in environmental studies by linking economic and environmental variables. The presentation begins by describing the fundamental aspects of input-output theory and its relevance to environmental concerns. It then provides a detailed but non-exhaustive exploration of various applications of input-output models in environmental modeling, addressing limitations and suggesting potential extensions of the model. The presentation concludes by providing an overview of the future direction of input-output models in the field of environmental analysis.