The focus of this study is to explore why public agencies implement enterprise architecture programs and the interoperability challenges they are faced with when governing these programs at different levels (vertical) and different functions (horizontal) of government. With a theoretical lens based on institutional theory from the political science field, the analysis shows that interoperability is not just a technical issue and that economic and political factors are just as important when implementing enterprise architecture programs in government. The findings suggest that implementing enterprise architectures in government challenge the way information systems are organized and governed in public agencies and calls for a broader definition of interoperability. The case study indicates that interoperability challenges arise because there is no overall coordination of different information systems initiatives in the health sector and because public hospitals have no economic and/or ...