In some embodiments the present invention provides influenza hemagglutinin ("HA") polypeptides, proteins, and protein complexes that comprise a stalk domain that is engineered to facilitate maintenance of its native trimeric conformation, even if the head domain of the HA protein is removed or disrupted. In some embodiments, the present invention provides compositions comprising such polypeptides, proteins, and protein complexes, and methods of use of such proteins and compositions, for example as vaccine immunogens.
