The Citizenship (Amendment) Act, 2019 (CAA) and National Register of Citizens (NRC) issue remains one of the most polarising and contentious topics in contemporary Indian politics. The CAA, passed in December 2019, provides a pathway to Indian citizenship for non-Muslim minorities who entered India on or before December 31, 2014, due to religious persecution. The NRC is a register that documents all legal citizens of India. While there is no specific provision in CAA or NRC for detention centres for unauthorised immigrants, these exist specifically under the Foreigners Act, 1946. Through this paper, the authors aim to examine the impact of CAA-NRC on such detention centres. The paper briefly introduces the concept of citizenship and then explores the rights-based approach to citizenship in India. Part I of the paper explains the CAA, its purpose, and the implications of its enactment on the citizenship status of ‘illegal migrants’. Part II discusses two other major provisions: the National Register of Citizens and the National Population Register, as well as their connection and relationship with the CAA. Part III of the paper examines the importance of the Foreigners Act, 1946, in the scheme of CAA, and how the two, when read together, will lead to ‘illegal migrants’ or ‘doubtful citizens’ landing in detention Centres. Part IV examines the International law regarding the legality of such detention centres and India’s compliance with it. Part V analyses the legality, working and establishment of such detention centres and the treatment of people housed therein from an International Law and International Human Rights Law perspective. Part VI examines the functioning of such detention centres in other developed jurisdictions worldwide. Lastly, the paper concludes by providing a way forward for the current system of detention centres in India.