Fundamental Duties were added to the Constitution by the 42nd Amendment, also known as the Constitution (Forty-second Amendment) Act, 1976.

Background:
The idea of adding Fundamental Duties to the Constitution was first proposed by the Swaran Singh Committee in 1976. The Committee recommended that a new chapter on Fundamental Duties be added to the Constitution, to emphasize the importance of civic responsibilities and to balance the rights available to citizens. The Committee also suggested that the Fundamental Duties should be enforceable by law, and that they should be made an integral part of the Constitution.

Features of the 42nd Amendment:
The 42nd Amendment of the Constitution was passed during the Emergency period, and it made several changes to the Constitution. Some of the important features of the 42nd Amendment are as follows:

- The amendment added a new Part IV-A to the Constitution, which contains the Fundamental Duties. This part consists of a single article, Article 51-A, which lists ten fundamental duties that every citizen of India should follow.
- The ten Fundamental Duties are as follows:
- To abide by the Constitution and respect its ideals and institutions, the National Flag, and the National Anthem;
- To cherish and follow the noble ideals which inspired the national struggle for freedom;
- To uphold and protect the sovereignty, unity, and integrity of India;
- To defend the country and render national service when called upon to do so;
- To promote harmony and the spirit of common brotherhood among all the people of India transcending religious, linguistic, and regional or sectional diversities;
- To renounce practices derogatory to the dignity of women;
- To value and preserve the rich heritage of our composite culture;
- To protect and improve the natural environment including forests, lakes, rivers, and wildlife, and to have compassion for living creatures;
- To develop the scientific temper, humanism, and the spirit of inquiry and reform; and
- To safeguard public property and to abjure violence.

- The amendment also made it clear that the Fundamental Duties are non-justiciable, which means that they cannot be enforced by a court of law. However, it is the duty of the State to promote these duties and to create conditions for their fulfillment.
- The 42nd Amendment also made several other changes to the Constitution, such as giving more powers to the Prime Minister, making it harder to challenge the validity of laws, and changing the name of the country from "India, that is Bharat" to "Bharat, that is India".

Conclusion:
The addition of Fundamental Duties to the Constitution was an important step in emphasizing the importance of civic responsibilities and balancing the rights available to citizens. Although the Fundamental Duties are non-justiciable, they serve as a reminder to citizens of their duties and responsibilities towards the nation. The 42nd Amendment, however, was criticized for its other changes to the Constitution, which were seen as undemocratic and authoritarian.