India observes Constitution Day on November 26 to mark the date in 1949 when the Constituent Assembly formally adopted the Constitution. The document came into force on January 26, 1950, the date celebrated as Republic Day. The Constitution is the world's longest written constitution, originally containing 395 articles, 8 schedules, and 22 parts. It draws from multiple sources, blending parliamentary democracy, fundamental rights, directive principles, and a unique federal structure with a strong unitary bias.

The Indian Constitution is simultaneously the supreme law of the land and a living document — it has been amended over 105 times since 1950, yet its basic structure remains judicially protected. Understanding its key features is not a memorisation exercise; it is a conceptual map that helps you identify why specific provisions exist and how courts have interpreted them.

The most exam-critical features are:

**1. Lengthiest Written Constitution:** Originally 395 articles, 8 schedules, 22 parts. Currently over 448 articles, 12 schedules, 25 parts after amendments. No other national constitution rivals this length — a product of conscious drafting by B.R. Ambedkar's committee drawing from the Government of India Act, 1935, and ten other constitutions.

**2. Federal with Unitary Bias:** India is described as a 'Union of States' (Art. 1), not a federation. During emergencies, it becomes effectively unitary. The Supreme Court in S.R. Bommai v. Union of India (1994) called federalism a basic structure feature — yet the centre retains overriding powers.

**3. Parliamentary Form of Government:** The executive is accountable to the legislature (Arts. 74–75), unlike the presidential model. The President acts on Cabinet advice.

**4. Fundamental Rights (Part III, Arts. 12–35):** Justiciable rights enforceable against the State. Art. 32 (right to move SC) is itself a fundamental right — Ambedkar called it the 'heart and soul' of the Constitution.

**5. Directive Principles (Part IV, Arts. 36–51):** Non-justiciable but fundamental to governance. In Minerva Mills (1980), the SC held that harmony between FRs and DPSPs is part of the basic structure.

**6. Basic Structure Doctrine:** Evolved in Kesavananda Bharati v. State of Kerala (1973) — Parliament cannot amend the Constitution so as to destroy its basic features.

Constitution Day itself was officially designated by the Government of India in 2015 to mark the 125th birth anniversary of Dr. B.R. Ambedkar.