Citizenship in India & Indian citizenship acts

Fundamental Rights provided in Indian constitution are available to citizens of India only; some of the fundamental rights which are not enjoyed by a non-citizen of India are:

Right to be discriminated on the basis of religion, race, sex, cast or birth of place
Equal opportunities in public employment
Right of six democratic freedoms (Article 19) + Cultural & educational rights

Only citizens of India have the right:

To hold civil office
Right to vote
Right to be judges of courts

Indian citizenship act, 1955

Indian constitution provides single citizenship to all irrespective of the states a person belongs to
Constitution simply describes classes of people deemed to be citizens of India as on 26th Jan 1950 & leaves entire law of citizenship to be regulated by parliamentary laws

Parliament enacted Indian citizenship act, 1955 for acquisition & loss of Indian citizenship. Since its commencement it has been amended four times:

The Citizenship (Amendment) Act, 1986.
The Citizenship (Amendment) Act, 1992.
The Citizenship (Amendment) Act, 2003.
The Citizenship (Amendment) Act, 2005.

According to Indian citizenship act, 1955, Indian citizenship was extended to citizens of commonwealth countries, but this law was repealed by amendment in 2003.

Acquisition of Indian Citizenship as per Citizenship act, 1955

Citizenship by birth: Every person born in India on or after January 26, 1950, shall be a citizen of India by birth.

Citizenship by descent: A person born outside India on or after January 26, 1950, shall be a citizen of India by descent if either of his parents is a citizen of India at the time of the person’s birth.

Citizenship by registration: A person can acquire Indian citizenship by registering themselves before the prescribed authority, e.g., persons of Indian origin who are ordinarily resident in India and have been so for five years immediately before making the application for registration; persons who are married to citizens of India.

Citizenship by naturalization: A foreigner can acquire Indian citizenship, on application for naturalisation to the Government of India.

Citizenship by Incorporation of territory: If any new territory becomes a part of India, the Government of India shall specify the persons of that territory as citizens of India.