The India-Nepal border is a 1,751 km long international boundary that runs between the two countries, traversing the Himalayan territories and the Indo-Gangetic Plain. Its modern delineation originates from the Treaty of Sugauli, signed on March 4, 1816, between the Kingdom of Nepal and the British East India Company following the Anglo-Nepalese War (1814–16). This treaty forced Nepal to cede territories and defined the western boundary along the Kali River.
The border's key characteristic is its status as an open international boundary, a mechanism institutionalized by the 1950 Treaty of Peace and Friendship. Articles 6 and 7 of the 1950 Treaty grant nationals of both countries reciprocal privileges, including the right to free movement, residence, and participation in trade and commerce in each other's territory, without the need for passports or visas. This arrangement fosters deep socio-cultural and economic ties, often referred to as Roti-Beti Ka Rishta.
The border has recently been a source of tension due to unresolved territorial disputes, particularly over the Kalapani, Lipulekh, and Limpiyadhura areas in the west, and the Susta area. The dispute in the west stems from the ambiguity in the 1816 Treaty of Sugauli, which did not clearly define the Kali River's origin, leading to differing interpretations of the boundary line. While approximately 98% of the boundary has been demarcated, these remaining segments require political resolution. Nepal's 2020 publication of a revised map including Kalapani, Lipulekh, and Limpiyadhura, and India's subsequent reaffirmation of its position, highlight the ongoing nature of the dispute. Security along the border is managed by India's Sashastra Seema Bal (SSB) and Nepal's Armed Police Force (APF).