Many viruses enter hosts by invading mucosal surfaces. Mammalian reoviruses gain access to the host by the gastrointestinal and respiratory tracts. Determinants of reovirus infection of the gastrointestinal tract are well- understood, however the host and viral determinants of respiratory reovirus infection are unknown. The work within this thesis characterizes the host and viral determinants of respiratory reovirus infection and systemic dissemination. To accomplish this, we developed a murine model of respiratory reovirus infection. Using this model, we showed that endogenous respiratory and inflammatory proteases can promote reovirus infection in vitro and that pre- existing inflammation augments in vivo infection in the murine respiratory tract. Through this work, we identified two laboratory isolates of T3D, T3DC and T3DF, that differ in their capacity to replicate in the respiratory tract and spread systemically, and we used these viruses to describe genetic polymorphisms that regulate reovirus replication and dissemination. The data presented in this thesis illustrate that reovirus infection of the respiratory tract and systemic dissemination are influenced by multiple factors including virion composition, resistance or sensitivity to protease-mediated inactivation and respiratory inflammation.