Avogadro is an advanced, cross-platform molecule editor and visualizer designed for computational chemistry, molecular modeling, bioinformatics, and materials science. It offers flexible, high-quality rendering and a powerful plugin architecture. The project aims to enhance the semantic accessibility of chemical data types by using the Chemical Markup Language (CML) as its native document format. The Avogadro library provides a code library and API with three-dimensional visualization capabilities, supporting research and education in chemistry, physics, materials science, and biology. The application and library can be extended using plugins in C++ or Python to explore different visualization techniques, build and manipulate molecular structures, and interact with other programs. Key features include building molecular structures, formatting input files, and analyzing output from various computational chemistry packages. Avogadro is freely available under an open-source license and has been cited over 100 times in various scientific applications.Avogadro is an advanced, cross-platform molecule editor and visualizer designed for computational chemistry, molecular modeling, bioinformatics, and materials science. It offers flexible, high-quality rendering and a powerful plugin architecture. The project aims to enhance the semantic accessibility of chemical data types by using the Chemical Markup Language (CML) as its native document format. The Avogadro library provides a code library and API with three-dimensional visualization capabilities, supporting research and education in chemistry, physics, materials science, and biology. The application and library can be extended using plugins in C++ or Python to explore different visualization techniques, build and manipulate molecular structures, and interact with other programs. Key features include building molecular structures, formatting input files, and analyzing output from various computational chemistry packages. Avogadro is freely available under an open-source license and has been cited over 100 times in various scientific applications.