Constitution of India was passed and adopted on 26th November 1949. This date is celebrated as Constitution Day or Samvidhan Divas in India. Here's a brief explanation:

Constitution Making Process:
- The Constitution of India was drafted by a Constituent Assembly that was formed in 1946 under the Cabinet Mission Plan.
- The Constituent Assembly was headed by Dr. Rajendra Prasad and had members from various political parties and regions.
- The drafting committee was headed by Dr. B.R. Ambedkar and had seven other members.

Adoption of the Constitution:
- The Constitution was adopted by the Constituent Assembly on 26th November 1949 after almost three years of deliberations, debates and modifications.
- The Constitution had a preamble, 395 articles and 8 schedules.
- The members of the Constituent Assembly signed two copies of the Constitution, one in English and one in Hindi.
- The Constitution came into effect on 26th January 1950, which is celebrated as Republic Day in India.

Significance of the Constitution:
- The Constitution of India is the supreme law of the land that provides a framework for governance, rights and duties of citizens and the functioning of the government.
- It is one of the longest written Constitutions in the world that reflects the diversity and unity of India.
- The Constitution has been amended several times over the years to keep pace with the changing times and needs of the society.

Conclusion:
The Constitution of India is a living document that reflects the aspirations and ideals of the people of India. It has played a crucial role in shaping India's democracy, secularism and unity in diversity. The adoption of the Constitution on 26th November 1949 is a significant milestone in India's history that is celebrated every year as Constitution Day.