Haemophilus influenzae is a Gram-negative bacterium that can cause otitis media, respiratory tract infections, and invasive disease. H. influenzae can be classified into two groups: strains with a polysaccharide capsule and strains without a capsule, or “nontypeable” H. influenzae (NTHi). While a vaccine targeting H. influenzae serotype b (Hib) exists and is highly effective, this vaccine has no effect on other encapsulated serotypes or NTHi. Hence, H. influenzae remains a significant health problem worldwide. The overall objective of this thesis was to address this problem by developing a vaccine that would elicit protection against all H. influenzae strains, regardless of capsule type or presence of capsule. To accomplish this, the iron acquisition protein transferrin binding protein B (TbpB), which helps to bind and remove iron from the host glycoprotein transferrin, was targeted. TbpB is an attractive vaccine candidate as it has been found to be essential for bacterial survival and pathogenesis in the host. In addition, since TbpB is present in both encapsulated H. influenzae and NTHi, a TbpB-based vaccine has the potential to confer protection against both groups. Our group has previously shown that engineered TbpBs and TbpB subdomains can elicit broadly cross-reactive antiserum and prevent bacterial infections by strains expressing heterologous TbpB variants. Phylogenetic and immunological analyses have also suggested that a vaccine containing representative variants from each phylogenetic cluster can provide comprehensive protection. Hence, in this thesis, I evaluate the hypothesis that a strategically engineered TbpB-based vaccine can confer protection against infection by both encapsulated H. influenzae and NTHi strains using two distinct vaccine design strategies – one in which a set of representative TbpBs was selected for inclusion in a multivalent vaccine and another involving the use of a single conserved TbpB subdomain. The antigens produced using these two strategies were then compared for their ability to elicit a cross-reactive antibody response and to confer protection against invasive challenge with H. influenzae. Overall, the results presented herein provide support for the use of conserved TbpB subdomains for eliciting broad protection and highlight important considerations for establishing animal infection models for evaluating vaccines.