Influenza, commonly known as the flu, is a highly contagious respiratory tract infection caused by influenza viruses. The virus is categorized into types A, B, C, and subtypes based on the surface proteins hemagglutinin (H) and neuraminidase (N). Influenza typically presents with sudden onset of symptoms such as fever, cough, sore throat, muscle aches, and fatigue. Complications can include pneumonia, exacerbation of pre-existing medical conditions, and, in severe cases, death. Influenza viruses undergo frequent genetic changes, leading to seasonal epidemics and occasional pandemics. Vaccination is a crucial preventive measure, with annual flu vaccines designed to match the prevalent virus strains. Antiviral medications like oseltamivir and zanamivir can be prescribed to reduce the severity and duration of symptoms if administered early in the course of the illness. Public health strategies for influenza include surveillance, vaccination campaigns, and education on hygiene practices to limit transmission. Ongoing research focuses on improving vaccine formulations, understanding viral evolution, and developing novel antiviral treatments to enhance our ability to combat influenza.