Neoclassical Realists broadly agree on the relative explanatory power of systemic- and domestic-level variables in determining foreign, defence and security policy outcomes. However, the theory is characterised by significant contestation about the nature of these systemic- and domestic-level variables. Disagreement exists about the role played by Waltz’s balance of power or Walt’s balance of threat at the systemic-level and about the impact of culture, nationalism, ideology and other, more material variables at the domestic-level. Using CSDP as a case study, this chapter argues that Neoclassical Realism’s explanatory power is enhanced when it integrates Walt’s ‘balance of threat’ approach, rather than Waltzian Neorealism. Furthermore, it demonstrates that Neoclassical Realism has the ability to account for the roles played by a variety of material and non-material variables at the domestic-level and opens up interesting possibilities for dialogue between cultural and realist approaches.