Rhinosinusitis represents a complicated and multifaceted group of diseases that is generally classified into the categories of acute and chronic. Although many instances of acute rhinosinusitis lasting longer than 7 days are thought to be of bacterial origin, most are thought to be inflammatory rather than infectious. The contribution of infectious organisms to the pathogenesis of chronic rhinosinusitis is an area of controversy and active investigation. Examples of these areas of investigation include biofilms, osteitis, and bacterial superantigens. This review discusses the role of infectious organisms in both acute and chronic sinusitis, with special focus on the etiology and diagnosis of these conditions, and includes a discussion of principles of their management.