The 87th Amendment Act is a constitutional amendment, officially titled The Constitution (Eighty-seventh Amendment) Act, 2003, which was enacted on June 22, 2003. Its primary purpose was to enable the readjustment and rationalization of territorial constituencies for the Lok Sabha and State Legislative Assemblies.
The amendment was created to solve a problem arising from the previous freeze on delimitation. The 42nd Amendment Act, 1976, had frozen the allocation of seats to states and the division of constituencies based on the 1971 Census figures until the year 2000, a measure intended to encourage population control. The 84th Amendment Act, 2001, extended this freeze on the total number of seats until 2026 but allowed for the internal readjustment of constituencies based on the 1991 Census.
The 87th Amendment Act, 2003, changed this by mandating the use of the population figures from the 2001 Census for the purpose of redrawing constituency boundaries. It works by substituting the figure "1991" with "2001" in the relevant articles of the Constitution. Specifically, it amended Article 82 (readjustment after each census), Article 170 (composition of Legislative Assemblies), and Article 330 (reservation of seats for Scheduled Castes and Scheduled Tribes in the Lok Sabha). This allowed the Delimitation Commission, constituted under the Delimitation Act, 2002, to rationalize the boundaries of existing constituencies and re-fix the number of seats reserved for SCs and STs based on the latest population data, without altering the total number of seats allocated to each state. The amendment came into effect on October 31, 2003.
The concept connects directly to the process of Delimitation and the principle of "one man, one vote, one value". It is related to the 84th Amendment Act, 2001, which it effectively replaced the census year for internal delimitation, and the ongoing freeze on the total number of seats, which is set to continue until 2026.