Abstract: The present disclosure relates to Moraxella catarrhalis outer membrane vesicle (OMV) compositions, to selected antigenic proteins from the outer membranes of M. catarrhalis which have a variety of useful properties, and to monoclonal antibodies against these proteins. Particular "Outer Membrane Proteins" (OMPs) of the invention are characterized as having molecular weights of about 30 kD, 80 kD (also termed CopB protein) and between about 200 and 700 kD (HMWP antigen). Passive immunization with monoclonal antibodies directed against these proteins confers protection against homologous and heterologous Moraxella catarrhalis strains in animal models, and active immunization with outer membrane vesicles also enhances pulmonary clearance of distinct M. catarrhalis strains. This demonstrates both the utility of antibodies in conferring passive immunity and the usefulness of OMPs, or variants thereof, in the preparation of vaccines.