The Land Boundary Agreement (LBA) is an international treaty between India and Bangladesh, which was given domestic effect in India through the Constitution (One Hundredth Amendment) Act, 2015. Its origin traces back to the cartographic chaos of the Radcliffe Award during the 1947 Partition, which left a complex, undemarcated border and numerous enclaves (or chhitmahals). The immediate basis was the Indo-Bangladesh Treaty signed by Indira Gandhi and Sheikh Mujibur Rahman on 16 May 1974, formally titled the Agreement Concerning the Demarcation of the Land Boundary between India and Bangladesh and Related Matters.
The LBA's purpose was to resolve three long-standing issues: the exchange of enclaves, the settlement of adverse possessions, and the demarcation of roughly 6.1 kilometres of undemarcated border. Implementation was delayed because the Supreme Court's 1960 ruling in In Re: The Berubari Union held that ceding sovereign territory requires a constitutional amendment under Article 368. The 1974 Agreement was updated by a 2011 Protocol.
The 100th Amendment Act, 2015, which received presidential assent on 28 May 2015, works by amending the First Schedule of the Constitution to reflect the territorial changes in the states of Assam, West Bengal, Meghalaya, and Tripura. Key provisions included India transferring 111 enclaves (17,160 acres) to Bangladesh and receiving 51 enclaves (7,110 acres) from Bangladesh. The agreement also gave residents of the exchanged enclaves a one-time choice of nationality. The physical transfer of enclaves became effective at midnight on 31 July 2015. The LBA connects to the earlier Nehru-Noon Agreement of 1958 with Pakistan, which was an attempt to resolve the same border issues.