TreeDyn is a tree visualization and annotation tool that allows the management and analysis of multiple trees. It uses annotations and dynamic graphical methods for editing and analyzing trees. The main features of TreeDyn include the management of multiple windows and trees, the export of graphics to various formats, the projection of texts or symbols on tree elements, the highlighting of graphical elements based on queries or selections, the highlighting of targeted trees according to a source tree, powerful scripts for automating tasks, a command line interpreter for online tree building, and a library of packages for specific research fields. TreeDyn is implemented in Tcl/Tk and is available for macOS, Linux, and Windows. It allows the import and export of trees from formats such as Nexus and Newick, and supports the creation of TGF files for saving and restoring graphical analysis. TreeDyn enables the management of collections of trees, allowing for the display, resizing, and configuration of multiple trees. It also supports the projection of annotations on tree elements, the identification of tree elements based on leaf labels or annotations, and the reflection of trees based on a source tree. TreeDyn provides scripting capabilities for automating repetitive tasks and allows the use of external annotation files to manage meta-information. It supports the visualization of trees in various formats, including Postscript, SVG, and HTML. TreeDyn also includes packages for specific tree-related tasks, such as TreeBASEinterf, TreeIG, TreePAT, and TreeXY. TreeDyn is under active development and is available under the GPL license. It is designed to be compatible with the basic Newick format and allows for the management of multiple trees and meta-information. TreeDyn is a powerful tool for the visualization and analysis of phylogenetic trees, providing a range of features for tree manipulation, annotation, and comparison.TreeDyn is a tree visualization and annotation tool that allows the management and analysis of multiple trees. It uses annotations and dynamic graphical methods for editing and analyzing trees. The main features of TreeDyn include the management of multiple windows and trees, the export of graphics to various formats, the projection of texts or symbols on tree elements, the highlighting of graphical elements based on queries or selections, the highlighting of targeted trees according to a source tree, powerful scripts for automating tasks, a command line interpreter for online tree building, and a library of packages for specific research fields. TreeDyn is implemented in Tcl/Tk and is available for macOS, Linux, and Windows. It allows the import and export of trees from formats such as Nexus and Newick, and supports the creation of TGF files for saving and restoring graphical analysis. TreeDyn enables the management of collections of trees, allowing for the display, resizing, and configuration of multiple trees. It also supports the projection of annotations on tree elements, the identification of tree elements based on leaf labels or annotations, and the reflection of trees based on a source tree. TreeDyn provides scripting capabilities for automating repetitive tasks and allows the use of external annotation files to manage meta-information. It supports the visualization of trees in various formats, including Postscript, SVG, and HTML. TreeDyn also includes packages for specific tree-related tasks, such as TreeBASEinterf, TreeIG, TreePAT, and TreeXY. TreeDyn is under active development and is available under the GPL license. It is designed to be compatible with the basic Newick format and allows for the management of multiple trees and meta-information. TreeDyn is a powerful tool for the visualization and analysis of phylogenetic trees, providing a range of features for tree manipulation, annotation, and comparison.