Here are the top 10 points in this big story:
Home Minister Amit Shah, tabling the Citizenship (Amendment) Bill in the Rajya Sabha, said Muslims of the country need not fear because "they are and will remain citizens of the country". Hitting out at what he called "attempts to spread misinformation", Mr Shah claimed that the bill was only for minority communities in neighbouring countries and had "nothing to do" with Muslims in India.
The Congress's Anand Sharma made an impassioned plea against the bill, saying that it "hurts the very soul of the Constitution of India". "I am convinced this bill is an assault on the very foundation of the Constitution of India. It hurts the very soul of the Constitution of India. It goes against the very preamble of the constitution," he said.
Trinamool Congress MP Derek O'Brien warned the Rajya Sabha that India was "moving from a democracy to a dictatorship". In his address, Mr O'Brien invoked images from Nazi Germany and compared them to the Citizenship Bill and the NRC, starting with an "eerie similarity" between concentration camps and detention camps in the North East.
The BJP's JP Nadda also spoke on the Citizenship Bill, vehemently denying the opposition's claims that the Citizenship Bill was discriminatory. "That is absolutely incorrect," he said, stressing that the proposed law was "purely for minorities in Pakistan, Afghanistan and Bangladesh". "It has nothing to do with Indians at all," he added.
Congress MP P Chidambaram, out on bail in the INX Media case after a prolonged legal struggle, posed several key questions to the centre, including asking why only three of India's neighbours had been considered in the bill and why other communities and faiths - such as Sri Lankan Hindus - have been excluded.
Even as the Rajya Sabha debated the matter, the Army was deployed to parts of Tripura and Assam to quell protests against the bill. Sources said two columns were dispatched to the Kanchanpur and Manu areas of Tripura and two others were sent to Bongaingon and Dibrugarh in Assam.
The Assam government has suspended mobile internet and data services in 10 districts of the state and imposed a curfew in Guwahati, the state's largest city. Guwahati has seen chaos of a magnitude unseen since the violent six-year movement by students that ended with the signing of the Assam accord in 1985.
On Monday, while defending the bill in the Lok Sabha, Amit Shah called for an end to protests by North-East states, saying appropriate measures have been made to ensure the region's identity would be intact. Protesters have expressed concerns refugees allowed by the bill could endanger identity and livelihood of indigenous people.
Earlier today Prime Minister Narendra Modi addressed BJP MPs and said "some parties" were speaking the same language as Pakistan on the Citizenship (Amendment) Bill. "Citizenship Bill will be written in golden letters, it will give permanent relief to people who fled religious persecution," he said.
Congress leader Rahul Gandhi launched a scathing attack on the bill and the centre today, terming it as a "criminal attack on the northeast" and an attempt by the centre to "ethnically cleanse" the region. A Lok Sabha MP, Mr Gandhi said he stood in solidarity with the people of the North East and was at their service.
With input from PTI