India’s most important tax reform since 1947 could finally become a reality this week.

Sixteen years after it was first mooted, the Goods and Services Tax (GST) might be passed this week by the Indian parliament, giving a big push to prime minister Narendra Modi’s reforms agenda. The GST will replace most indirect taxes in Asia’s third-largest economy.

Since coming to power in May 2014, Modi has pushed hard to get India’s lawmakers to approve the key reform. But due to opposition, mainly from the Congress party, it was delayed by two more years. Ironically, it was the Congress party that had aggressively pushed for the GST while it was in power between 2009 and 2014.

India’s tax system presently consists of direct taxes, such as the income tax, and indirect taxes, comprising numerous central and state levies such as value added tax, sales tax, octroi and luxury tax. The GST will bring these indirect taxes under one umbrella. The rate of the tax is still unknown but various news reports peg it at between 15% and 18%.

As Quartz explained earlier, the GST would make it “economically efficient” for multinational companies, which compete with India’s unorganised sector, “as it simplifies the indirect tax structure to one general rate.”

On Aug. 03, the Rajya Sabha, the upper house of India’s parliament, will debate the GST Constitutional Amendment Bill. The lower house, Lok Sabha, passed the bill last May but the Rajya Sabha’s approval is necessary for it to become a law.

To get the bill through parliament, the Modi government has agreed to four crucial amendments to the bill. This seems to have helped it turn the tide in its favour. These amendments include getting rid of a 1% tax that the centre was to levy on interstate trade, and compensation to states for the loss they would incur in the first five years once the GST is implemented.

The GST will, however, not include taxes on petroleum products, electricity duties, excise duty on alcohol, and stamp duty on immoveable property from its purview. That’s because these taxes provide substantial revenue to state governments.

“The impetus to move towards GST stems from the inadequacies of the present system and the need for a taxation system that is economically efficient, neutral in its implication, simple to administer, encourages voluntary compliance and, most importantly, integrates India to a single common market,” Morgan Stanley economists explained in a report last week.

Here is how the GST has evolved over the past 16 years.

2000: Atal Bihari Vajpayee, then prime minister of India, flags off discussions on the GST. He sets up a committee headed by the then finance minister of West Bengal, Asim Dasgupta, to design the GST model and put in place the back-end technology and logistics for its implementation. Dasgupta remained the chairman of the committee until 2011.

2004: A task force chaired by Vijay L. Kelkar, then advisor to the finance ministry, says the existing tax system suffers from many problems. It suggests a comprehensive GST.

February 2005: In his budget speech for financial year 2005-06, the then finance minister Palaniappan Chidambaram says: “In the medium-to-long term, it is my goal that the entire production-distribution chain should be covered by a national VAT (value added tax), or even better, a goods and services tax, encompassing both the centre and the states.”

February 2006: Chidambaram sets April 1, 2010, as the date for introducing the GST. “(The) world over, goods and services attract the same rate of tax. That is the foundation of a GST. People must get used to the idea of a GST,” he says.

November 2006: Parthasarthy Shome, adviser to finance minister Chidambaram, says states will have to take various reform measures to pave the way for the GST. “At the moment, the issue of discussion between the state and the centre is compensation for central sales tax,” Shome says.

February 2007: The union budget for 2007-08 retains the April 1, 2010 deadline for implementation of the GST.

February 2008: While reading out the union budget for 2008-09, the finance minister Chidambaram says, “I am also happy to report that there is considerable progress in preparing a roadmap for introducing the Goods and Services Tax with effect from April 1, 2010.”

July 2009: India’s new finance minister, Pranab Mukherjee, announces the basic structure for the GST. The government retains the April 1, 2010, deadline.

November 2009: The committee under Asim Dasgupta releases its first discussion paper on the GST in the public domain, looking to generate a debate and obtain inputs from stakeholders.

February 2010: The government launches a mission-mode project for the computerisation of commercial taxes in states which is expected to lay the foundation for the GST. The budgetary outlay for the project is Rs1,133 crore, of which the centre’s share is Rs800 crore. The GST implementation is pushed back by another year. “I am confident that the government will be in a position to implement DTC (direct tax code) from April 1, 2011,” finance minister Mukherjee says.

March 2011: The Congress party-led government introduces a constitution amendment bill in the Lok Sabha to implement GST. India’s opposition parties protest. The bill is sent to a parliamentary standing committee headed by former finance minister Yashwant Sinha. A bill is usually sent to the standing committee—that comprises members from Lok Sabha and Rajya Sabha—for a detailed examination.

June 2012: The standing committee begins discussion. India’s opposition parties, including the BJP and the Left, raise concerns over clause 279B which allows the centre to have extra discretionary powers over the GST dispute authority.

November 2012: Finance minister Chidambaram holds meetings with state finance ministers. The two sides set December 31, 2012 as the deadline to solve all issues.

February 2013: In his budget speech, Chidambaram announces that the government has made provisions of Rs9,000 crore for compensation to states. “I hope we can take this consensus forward in the next few months and bring to this house a draft bill on the constitutional amendment and a draft bill on the GST. I appeal to the state finance ministers to realise the serious intent of the government to introduce GST and come forward to work with the government and bring about a transformational change in the tax structure of the country,” Chidambaram says.

August 2013: The standing committee submits its report to parliament. The panel approves the legislation with some amendments on the provision of tax structure and resolution mechanism. ”What should be included in the laws and rules should not form part of the constitution of India. The present bill relating to GST, in the committee’s view, has not been well drafted from this perspective and, therefore, require amendments as suggested,” the report said.

October 2013: The Narendra Modi-ruled state of Gujarat opposes the bill. “If the union government, through an ordinance, enacts the GST regime, Gujarat will have to bear Rs14,000 crore loss per annum due to the destination-based taxation principle,” Saurabh Patel, a minister in Modi’s government, says.

May 2014: The constitution amendment bill lapses with the dissolution of the 15th Lok Sabha. The same month, the BJP, led by Narendra Modi, is voted into power.

December 2014: Seven months later, India’s new finance minister, Arun Jaitley, introduces the bill in the parliament. The Congress party, now in opposition, demands that the bill be sent to a standing committee.

February 2015: In his budget speech, Jaitley announces that the government is keen on implementing the GST by April 1, 2016 and hopes it will be cleared by parliament.

May 2015: The Lok Sabha passes the constitution amendment bill to GST. “I straight away concede that 27% (revenue-neutral rate) would be very high. We have decided to keep petroleum out and every state finance minister is not interested in imposing higher taxes on its own people, and neither the central government. Therefore, this figure is going to (get) much more diluted compared to the figure (27%) which has been mentioned,” Jaitley says.

August 2015: The government is unable to push the bill in the Rajya Sabha where it does not have a clear majority. ”Parliament disruption is frustrating for the whole country. This was a disruption without a cause,” Jaitley tells the media on Aug. 13.

March 2016: Jaitley says he agrees with the Congress’s demand that the GST rate must not be above 18%. But he disagrees that the rate should be fixed since “unforeseen emergencies” would require the government to raise the rate of tax in the future. If the government fixes a particular rate in the bill, it will have to take parliament’s permission each time it wants to raise the tax.

August 2016: The Congress seems to finally agree with the Modi government after it agrees to the four broad amendments to the bill. ”All the issues we have raised are there in the GST constitutional amendment,” Anand Sharma, a former minister for commerce and a senior Congress leader, tells NDTV. ”On the capping (on GST rate), we still want ring-fencing and (the) states to come to an agreement with the centre.”