The ade4 package in R provides a comprehensive set of multivariate analysis methods for ecological data, based on the duality diagram approach. This approach, rooted in the French school of "Analyse des Données," uses a unifying mathematical tool to analyze ecological data. The duality diagram allows for the simultaneous analysis of variables and individuals, enabling the identification of patterns and relationships in ecological communities. The package includes functions for various multivariate methods, such as principal component analysis (PCA), correspondence analysis, and RLQ analysis, which are implemented using the duality diagram framework. The package also includes tools for matrix approximation, inertia decomposition, and biplot visualization. The duality diagram theory is implemented in the ade4 package through a series of functions that perform eigendecompositions and generate results for ecological data analysis. The package is used to analyze environmental data, such as the dune meadow dataset, and provides insights into ecological patterns and relationships. The ade4 package is a valuable tool for ecologists to analyze and visualize complex ecological data.The ade4 package in R provides a comprehensive set of multivariate analysis methods for ecological data, based on the duality diagram approach. This approach, rooted in the French school of "Analyse des Données," uses a unifying mathematical tool to analyze ecological data. The duality diagram allows for the simultaneous analysis of variables and individuals, enabling the identification of patterns and relationships in ecological communities. The package includes functions for various multivariate methods, such as principal component analysis (PCA), correspondence analysis, and RLQ analysis, which are implemented using the duality diagram framework. The package also includes tools for matrix approximation, inertia decomposition, and biplot visualization. The duality diagram theory is implemented in the ade4 package through a series of functions that perform eigendecompositions and generate results for ecological data analysis. The package is used to analyze environmental data, such as the dune meadow dataset, and provides insights into ecological patterns and relationships. The ade4 package is a valuable tool for ecologists to analyze and visualize complex ecological data.