Gardnerella vaginalis has been considered a pivotal player in the progression of bacterial vaginosis (BV), a condition associated with serious health complications. However, G. vaginalis is also commonly found in asymptomatic or BV-negative women. This has generated interest in the question of whether genetic differences among isolates might distinguish pathogenic from commensal isolates. G. vaginalis was the only recognized species in its genus for four decades, but recently an emended description of G. vaginalis and descriptions of three new species - Gardnerella leopoldii, Gardnerella piotii, and Gardnerella swidsinskii - have been proposed. This review provides background on the heterogeneity and diversity within the genus Gardnerella, highlighting the main features that distinguish species and clades, and how these features may impact BV development.