Neisseria is a genus of bacteria that includes several species, some of which are important human pathogens. The most well-known species are Neisseria gonorrhoeae, which causes gonorrhea, and Neisseria meningitidis, responsible for meningococcal disease. These bacteria are typically found in pairs and are characterized by their spherical shape. These bacteria are gram-negative, meaning they do not retain the crystal violet stain used in the Gram staining procedure. Neisseria species thrive in warm, moist environments, often colonizing the mucous membranes of the human body, particularly in the respiratory and urogenital tracts.