Legionnaires' disease (LD) is a severe form of community-acquired pneumonia (CAP) caused by Legionella species, particularly Legionella pneumophila. It is underdiagnosed but increasingly common, with a mortality rate ranging from 4% to 40%, especially in immunocompromised patients or those requiring ICU admission. Recent advances in diagnosis, including urine antigen testing (UAT) and molecular methods, have improved detection. LD is associated with severe lung injury, extrapulmonary symptoms, and non-specific laboratory findings. The pathogenesis involves Legionella's ability to survive within macrophages and evade immune responses. The disease is linked to environmental factors, such as water systems, and is more prevalent in certain regions. Diagnosis is challenging, and while UAT is widely used, it has limitations in detecting non-Lp1 strains. PCR methods can detect all Legionella species and serogroups. Treatment typically involves macrolides, quinolones, or combinations, with prolonged therapy in severe cases. Mortality is influenced by factors such as ICU admission, immune status, and nosocomial source. Immune responses, including hyperinflammation and immunoparalysis, may contribute to disease severity. Research is needed on biomarkers, host-directed therapies, and optimal treatment regimens. The incidence of LD is rising, highlighting the need for improved diagnostic tools and targeted therapies. Future studies should focus on understanding the immune response, environmental factors, and the role of antibiotic resistance in LD management.Legionnaires' disease (LD) is a severe form of community-acquired pneumonia (CAP) caused by Legionella species, particularly Legionella pneumophila. It is underdiagnosed but increasingly common, with a mortality rate ranging from 4% to 40%, especially in immunocompromised patients or those requiring ICU admission. Recent advances in diagnosis, including urine antigen testing (UAT) and molecular methods, have improved detection. LD is associated with severe lung injury, extrapulmonary symptoms, and non-specific laboratory findings. The pathogenesis involves Legionella's ability to survive within macrophages and evade immune responses. The disease is linked to environmental factors, such as water systems, and is more prevalent in certain regions. Diagnosis is challenging, and while UAT is widely used, it has limitations in detecting non-Lp1 strains. PCR methods can detect all Legionella species and serogroups. Treatment typically involves macrolides, quinolones, or combinations, with prolonged therapy in severe cases. Mortality is influenced by factors such as ICU admission, immune status, and nosocomial source. Immune responses, including hyperinflammation and immunoparalysis, may contribute to disease severity. Research is needed on biomarkers, host-directed therapies, and optimal treatment regimens. The incidence of LD is rising, highlighting the need for improved diagnostic tools and targeted therapies. Future studies should focus on understanding the immune response, environmental factors, and the role of antibiotic resistance in LD management.