What FIDUCIA explores potential influences of Lutheran theology on the development of Danish trust culture. The Danish welfare state is characterised by high levels of social and institutional trust, which nourish a socially cohesive society with low corruption, a minimum of bureaucracy, and limited 'free-riding', despite high taxes. This trust culture has attracted considerable international attention, but little is known about its historical background. FIDUCIA unearths the possible theological roots hereof, examining how theological social imaginaries of trust might have affected how Danes related to fellow citizens, societal institutions, and state authorities as Denmark developed from an absolutist kingdom to a nascent liberal democratic welfare state from the mid-19th century onwards. Why FIDUCIA investigates the interplay between confessional culture and societal development by pioneering the question of theological influence on Danish trust culture and welfare state formation. FIDUCIA broadens the scope of welfare state research to include theological determinants and contributes to the budding interdisciplinary research on trust in which a theological perspective, despite its obviousness has not yet been applied. Additionally, FIDUCIA rethinks systematic theology to include conceptual analyses of trust central to both theology and society in an approach of 'theological conceptual history', which facilitates research on the complex connection between theological theorising and societal development. How FIDUCIA analyses a variety of material (e.g. legislation, theological texts, contributions to the public debate) and examines changes in the dynamics of trust in God, state authorities, and citizens, focusing on three historical cases: 1) The 1830s and 40s, when the absolutist kingdom evolved into a democracy and citizens arose as trustworthy authorities with constitutional rights and obligations, potentially challenging the trust relation between king and people; 2) The 1930s and 40s, when social reforms secured rights to benefits, and the threat and realisation of German occupation challenged the Danish democracy and nascent welfare state, endangering social trust; 3) The formation of the genuine welfare state in the late 1960s and early 70s, when social benefits were extended to all. SSR FIDUCIA answers to an impending international trust crisis. Trust in politicians, democratic institutions, and general community has decreased, the corona and climate crises challenge the fundamental trust in a sustainable future, and trust culture and trust-based democratic societies can no longer be taken for granted. In-depth knowledge of the religious background for Danish trust culture will help us understand the historical development of the trust culture undergirding the welfare state and, potentially, contribute to its future persistence. The historical examination serves as background for a contemporary perspective examining to what extent social imaginaries of trust rooted in Lutheran theology continue to nourish a trust mentality in one of the world's allegedly most secularized countries.