The article introduces Greengenes, a 16S rRNA gene database and workbench compatible with ARB. It addresses the limitations of public repositories by providing chimera screening, standard alignment, and taxonomic classification using multiple published taxonomies. The database identifies putative chimeras in 3% of environmental sequences and 0.2% of isolates, and classifies environmental sequences into 100 phylum-level lineages in Archaea and Bacteria. Greengenes offers standardized descriptive fields, taxonomic assignment, chimera screening, and ARB compatibility. It maintains a consistent multiple-sequence alignment (MSA) and tracks multiple taxonomies to promote user awareness of phylogenetic descent. The database is updated periodically and can be accessed through a web interface or imported directly into ARB for advanced analyses. The article also discusses the challenges of chimera detection and the importance of standardized classification in environmental surveys and 16S rRNA microarray design.The article introduces Greengenes, a 16S rRNA gene database and workbench compatible with ARB. It addresses the limitations of public repositories by providing chimera screening, standard alignment, and taxonomic classification using multiple published taxonomies. The database identifies putative chimeras in 3% of environmental sequences and 0.2% of isolates, and classifies environmental sequences into 100 phylum-level lineages in Archaea and Bacteria. Greengenes offers standardized descriptive fields, taxonomic assignment, chimera screening, and ARB compatibility. It maintains a consistent multiple-sequence alignment (MSA) and tracks multiple taxonomies to promote user awareness of phylogenetic descent. The database is updated periodically and can be accessed through a web interface or imported directly into ARB for advanced analyses. The article also discusses the challenges of chimera detection and the importance of standardized classification in environmental surveys and 16S rRNA microarray design.