Leptospira spp. are unique bacteria that are widespread in the environment and cause leptospirosis, a zoonotic disease transmitted through contact with contaminated water or soil. The genus Leptospira has been reclassified based on whole-genome sequencing, revealing 64 species, with 22 identified in 2018 and 64 in 2019. The genus is divided into two clades: "Saprophytes" and "Pathogens," with the latter containing species responsible for infections. Subclades P1 and S2 include various species, some of which may not be true pathogens. Leptospirosis is caused by pathogenic Leptospira species, such as L. interrogans, and is responsible for over a million cases and 60,000 deaths annually. Transmission occurs through contact with contaminated water or soil, and the severity of the disease depends on the virulence of the pathogen, the dose of infection, and host factors. Despite its high burden, leptospirosis is not recognized as a neglected tropical disease, and research remains limited due to lack of funding and interest. Leptospira has developed strategies to evade the immune system, including the use of endoflagella to cross cell barriers and disseminate in the host. The genome of Leptospira consists of two chromosomes and some plasmids, and genomic studies have revealed differences between pathogenic and non-pathogenic species, suggesting that pathogens evolved from free-living ancestors. Understanding the biology and virulence factors of Leptospira is crucial for developing effective treatments and prevention strategies.Leptospira spp. are unique bacteria that are widespread in the environment and cause leptospirosis, a zoonotic disease transmitted through contact with contaminated water or soil. The genus Leptospira has been reclassified based on whole-genome sequencing, revealing 64 species, with 22 identified in 2018 and 64 in 2019. The genus is divided into two clades: "Saprophytes" and "Pathogens," with the latter containing species responsible for infections. Subclades P1 and S2 include various species, some of which may not be true pathogens. Leptospirosis is caused by pathogenic Leptospira species, such as L. interrogans, and is responsible for over a million cases and 60,000 deaths annually. Transmission occurs through contact with contaminated water or soil, and the severity of the disease depends on the virulence of the pathogen, the dose of infection, and host factors. Despite its high burden, leptospirosis is not recognized as a neglected tropical disease, and research remains limited due to lack of funding and interest. Leptospira has developed strategies to evade the immune system, including the use of endoflagella to cross cell barriers and disseminate in the host. The genome of Leptospira consists of two chromosomes and some plasmids, and genomic studies have revealed differences between pathogenic and non-pathogenic species, suggesting that pathogens evolved from free-living ancestors. Understanding the biology and virulence factors of Leptospira is crucial for developing effective treatments and prevention strategies.