This article traces the development of the federal structure of Swiss citizenship between the founding of the federal state in 1848 and the entrenchment of a restrictive naturalisation and establishment policy in the interwar period. Considering the difficult integration of foreign residents through naturalisation in the past and present in Switzerland, the author examines the causes for the granting and refusal of Swiss citizenship. She shows that the development of and arrangements for access to Swiss citizenship cannot be reduced only to notions about the Swiss nation or national interests. They are the result of a permanent process of political negotiation and coordination between the federation, cantons and local authorities; owing to its importance in social assistance matters, local citizenship constituted an impediment to naturalisation until well into the twentieth century. In contrast, the federation and certain cantons like Zurich, Basle and Geneva had sought since the 1880s to reduce the strongly increasing number of foreign residents by liberalising naturalisation. The outbreak of the Second World War put an end to these endeavours. With the rise of a 'new right' since 1900, the setting up of the Central Office of the Foreign Police in 1917, and the institutionalisation of the authorities' 'fight against foreign infiltration', Swiss nationality law became ethnicised. Cultural 'assimilation' into the 'particularity of Swiss society' was now regarded as a precondition for becoming a Swiss citizen. The new federal rejection of foreigners thus joined with the traditionally restrictive policy of local authorities in an unholy alliance that began to breach only in the 1980s.