Leptospira interrogans, the causative agent of leptospirosis, consists of numerable serotypes capable of causing a variety of disease manifestations in a wide range of hosts. This motile and flagellated spirochete bacterium is recognizable via microscopy and earned its name from a characteristic hooked appearance that resembles a question mark. The taxonomic classifications within the Leptospira genus have been reorganized many times in accordance with new antigenic, genomic, and pathologic data. What was once over 250 serovars grouped into two Leptospira species is now 21 genomospecies of Leptospira with reclassified serovars. While the new taxonomic names are typically used in the scientific literature, historical names still circulate on product labels and in common use.