Krona is an interactive metagenomic visualization tool designed to explore the hierarchical relationships and abundances of taxonomic or functional groups within metagenomic data. It combines radial, space-filling displays with parametric coloring and polar-coordinate zooming, enabling intuitive exploration of complex hierarchies. The tool is implemented using HTML5 and JavaScript, allowing it to be fully interactive and accessible through any modern web browser without the need for additional software or plug-ins. Each chart can be an independent document, facilitating easy sharing via email or web servers. Krona addresses the limitations of existing visualization tools by providing a comprehensive view of abundance estimates and prediction confidence, making it a powerful tool for interpreting metagenomic analyses. The tool is also designed to be flexible and adaptable to new analysis methods, with its rendering code and conversion tools available under a BSD open-source license.Krona is an interactive metagenomic visualization tool designed to explore the hierarchical relationships and abundances of taxonomic or functional groups within metagenomic data. It combines radial, space-filling displays with parametric coloring and polar-coordinate zooming, enabling intuitive exploration of complex hierarchies. The tool is implemented using HTML5 and JavaScript, allowing it to be fully interactive and accessible through any modern web browser without the need for additional software or plug-ins. Each chart can be an independent document, facilitating easy sharing via email or web servers. Krona addresses the limitations of existing visualization tools by providing a comprehensive view of abundance estimates and prediction confidence, making it a powerful tool for interpreting metagenomic analyses. The tool is also designed to be flexible and adaptable to new analysis methods, with its rendering code and conversion tools available under a BSD open-source license.