This volume reviews the current understanding of the taxonomy, disease syndromes, genetics, biology, and pathogenic factors of Histophilus somni, as well as the host immune response to this pathogen. H. somni is one of the most important bacterial pathogens in cattle and other ruminants, and its virulence factors are highly conserved with Haemophilus influenzae and other members of the Pasteurellaceae. H. somni has been recognized as a major cause of thrombotic meningoencephalitis, respiratory disease syndromes, myocarditis, reproductive disease...