The purpose of this dissertation is to examine the burden-sharing behavior of new NATO members and the impact of enlargement on NATO burden-sharing. Qualitative and quantitative methods are used to test several hypotheses. The findings suggest that large NATO members are burden-sharing at a greater rate than smaller NATO members when looking at military expenditures and air contributions to NATO missions, in accordance with the logic of collective action. Contribution of troops to NATO missions depends on the mix of private and public benefits received, in accordance to the joint product model. The findings support the hypothesis that new NATO members are burden-sharing at a greater rate than older NATO members. An analysis of the burden-sharing behavior of NATO's new members reveals that new NATO members have demonstrated the willingness to contribute to NATO missions, but are often constrained by their limited capabilities. However, new member contributions to NATO have improved and, in comparison to older NATO members, the new members are doing quite well. Finally, NATO expansion did not lead to greater free-riding behavior in NATO. / Political Science