While liberalization has made great strides in both airlines and airports, the third, critical, component of the air transportation system still lags behind: air navigation services, and the entities that supply them, the air navigation service providers. Still, since New Zealand first started experimenting with commercialization in 1987, the air navigation services industry around the world has evolved tremendously. From being traditionally provided by the government or the military, air navigation service providers now come in a variety of institutional arrangements, including government corporations, non-profit private entities and public–private partnerships. This chapter explores those changes and their impacts, with a focus on two case studies in North America: the US and Canada. These are two interesting contrasting ANSPs: one that underwent institutional reform (Canada) and one that did not (US).