The annual flu season causes thousands of deaths and millions of hospitalizations, which pose a great burden to global health and economy. Moreover, a flu pandemic arising from reassortment viruses, such as H5N1 and H1N1, raises even greater concern due to the lack of effective vaccines at the initial stage of flu outbreak. The influenza virus is the causative agent of flu infection. Currently there are four drugs in use to combat influenza infection. Amantadine and rimantadine are M2 proton channel blockers that inhibit virus uncoating; oseltamivir and zanamivir are neuraminidase (NA) inhibitors that inhibit virus release. However, recent years have witnessed a drastic increase in instances of drug resistance, and flu strains that are resistant to both classes of drugs have been reported. Thus, there is a pressing need to develop the next generation of anti-influenza drugs. Among a handful of anti-influenza drug targets, the viral fusion protein hemagglutinin (HA) is one of the most advanced. This review discusses the biological roles of HA during viral replication and highlights peptide- and small molecule–based HA inhibitors, including recent computationally designed HA binders. The text is organized into four sections based on the maturation stages of HA: inhibitors targeting the glycosylation of HA, the proteolytic activation of HA, the attachment of HA to host cell receptors, and peptide- and small molecule–based inhibitors targeting HA-mediated membrane fusion. Of particular interest are advances in the areas of developing dual inhibitors targeting both HA and NA and broad-spectrum HA inhibitors targeting both groups of HAs.