The order , belonging to class , is globally distributed in various ecosystems. Currently, this order comprised 12 families that show vast phenotypic, ecological and genotypic variation. The classification of at the family level is currently mainly based on 16S rRNA gene sequencing analysis and the presence of shared phenotypic characteristics, resulting in noticeable anomalies. Our present study revises the taxonomy of based on 1080 available high-quality genome sequences of type strains. The evaluated parameters included the core-genome phylogeny, pairwise average aa identity, lineage-specific core genes, physiological criteria and ecological parameters. Based on the results of this polyphasic approach, we propose that the order be reclassified into 41 families, which include the existing 12 families, 17 families in a recent Validation List in the (Validation List no. 215) and 12 novel families for which we propose the names , , , , , , , , , , and . This work represents a genomic sequence-based and systematic framework for classifying the order at the family level, providing new insights into its evolution.