The invention discloses the Moraxella catarrhalis outer membrane protein polypeptide and polypeptides derived therefrom (collectively "OMP21"), nucleotide sequences encoding said OMP21, and antibodies that specifically bind OMP21. Also disclosed are pharmaceutical compositions including prophylactic or therapeutic compositions, which may be immunogenic compositions including vaccines, comprising OMP21, antibodies thereto or nucleotides encoding same. The invention additionally discloses methods of inducing an immune response to M. catarrhalis and OMP21 in an animal, preferably a human, methods of treating and methods of diagnosing Moraxella infections in an animal, preferably a human, and kits therefor.