What is the nature of popular nationalist sentiment within sub-state territories? Researchers discuss the impact that nationalism can have on politics regularly, yet their approaches to studying nationalism tend to differ greatly. Many scholars of nationalism focus on political elites, particularly when it comes to analysing sub-state territories. This is an issue for two reasons. First, there is no guarantee that individuals will echo the positions of elites. Second, nationalism can emerge prior to their mobilisation by elites. Attempts to address this either focus on micro-interactions that are difficult to generalise or operationalise (state-level) nationalism in a narrow (often exclusive) sense. Some scholars now attempt to bridge this gap by taking an inductive approach to capturing nationalism. However, these scholars tend to focus on the state and there is no guarantee that state-level analyses will apply within specific sub-state territories. There are several scholars who examine sub-state territories, but these analyses tend to focus on relative state/sub-state identities, rather than nationalism. It is this gap that I fill here. Consequently, the principal contribution of the thesis an investigation of popular nationalist sentiment within sub-state territories. Through this, I introduce a novel operationalisation of popular nationalist sentiment within sub-state territories. I then use this approach to answer three related research questions. How stable is popular nationalist sentiment within sub-state territories? What characteristics of a sub-state territory associate with the presence of popular nationalist sentiments? Does popular nationalist sentiment associate with other political attitudes within sub-state territories? Each of these questions relate to important debates within the existing literature on nationalism, and I demonstrate that my approach is a viable method of investigating them within sub-state territories. As a result, my thesis has important implications for how researchers investigate popular nationalist sentiment within sub-state territories.