Academic disciplines demarcate, organise, and structure specific branches of knowledge. From a sociological perspective, they regulate reward structures and labour markets through the allocation of prestige and status. Disciplines emerged simultaneously with the modern research university and the establishment of a formalised system for scholarly communication. The establishment of modern disciplines as the principal unit for organising knowledge in academia is largely a history of formalisation, stabilisation, and bureaucratisation. The importance of disciplines as areas for knowledge generation has weakened over time, but their role in guiding how knowledge is disseminated, stabilised, and transferred remains. While many disciplines are rather stable in their organisation, they are also continuously challenged as new fields emerge, while others disappear. Their importance for how academic knowledge is conducted, taught, organised, and evaluated remains however strong, and an understanding of how disciplines function is essential for anyone aiming to study the production of academic knowledge.