This document summarizes information about influenza and the H1N1 virus. It discusses the virology of influenza, past pandemics, seasonal flu trends, the emergence and characteristics of H1N1, and treatment and vaccination strategies. Regarding H1N1 specifically, it notes that while not especially virulent, it has spread widely due to lack of preexisting immunity in most populations. Looking ahead, a significant second wave is expected in the fall. Vaccination is the recommended strategy to reduce illness burden from this new strain of influenza.