The article traces the historical evolution of an understudied area of International Humanitarian Law (IHL): the rules on allegiance during occupation. By mapping state practice and scholarly opinions, the article shows the abandonment of the automatic transfer of the population’s allegiance to the occupant in favour of other theories. Nonetheless, the discussions surrounding this topic show a general struggle to label the relation between inhabitants and occupiers, and a general rejection of any theory that directly or indirectly presumes sovereignty of the occupier over the inhabitants. The article presents an element that is rarely included in debates on allegiance and occupation, i.e. the efforts of states to reinforce their sovereignty over occupied population through criminal prosecution of those who collaborated with the occupant. Finally, contemporary practice aimed at bypassing the regulations is presented as in-congruent with the rules regarding occupation in the Geneva Conventions. Despite the landmarks achieved in regulating the matter, the article shows that many aspects remain under discussion and formation. Furthermore, many current rules, practices and discussions only serve the interests of states and are oblivious of the hardships faced by individuals under occupation.