Here are the 10 points:
In the five years that the Supreme Court has been hearing the initial petition, the number of people issued Aadhaar numbers have gone up from 20-25 crore in 2012 to 119 crore, which ascribe unique ID numbers, and record fingerprints and iris scans of each person.
The case was held up because the central government contended that the top court had not always held privacy to be fundamental rights. This led the court to set up a nine-judge bench to first decide if privacy was a fundamental right or not.
Once this verdict came in, Chief Justice Dipak Misra set up this five-judge constitution bench to decide if any aspect of the Aadhaar programme including the law violated the fundamental right.
The other judges in the five-judge bench are Justices AK Sikri, AM Kanwilkar, DY Chandrachud and Ashok Bhushan.
"We are of the considered view that the resolution of the issues raised before the Court should proceed at the earliest...This will ensure clarity for citizens on the one hand and for the Union and the state governments and the instrumentalities on the other hand," the court had observed in December.
Critics say the Aadhaar identity enables government and private bodies to link enough data to allow profiling because it creates a comprehensive profile of a person's spending habits, friends and acquaintances, property and other such data.
Aadhaar was set up to be a secure form of digital identification for citizens, one that they could use for government services. The project was initially carried out through executive orders and was voluntary.
The Supreme Court in 2013 prevented the government from forcing people to submit their Aadhaar number to access welfare schemes. The NDA government worked around this restriction by getting parliamentary approval for the law in 2016 that gave it wide powers.
Aadhaar was launched by the previous UPA in 2009-10 to reduce the government's subsidy bill and remove duplicates from the home ministry-driven national population register that was inspired by BJP patriarch LK Advani's identity card project. After Prime Minister Narendra Modi came to power in 2014, the government put the population register on hold and put its weight behind Aadhaar.
PM Modi also mandated that new-borns too be issued the number, not just children after they turn five. This would make the number, issued after a person's fingerprints and iris, a cradle to grave digital identity for every resident.