To its supporters, the Trans-Atlantic Trade and Investment Partnership (TTIP) being negotiated by the United States and the European Union offers the chance to remove barriers to free up vital trade lines that will boost economies and provide many new jobs.
To its opponents, TTIP will take more shackles off big business whose unchecked actions will harm society, workers and public services and leave European governments with their hands tied.
The proposed deal has proved so divisive that the European Commission, which is leading the EU's talks with the US, launched a public consultation amid accusations from its critics that the process was secretive and undemocratic.
Since February last year, the two sides have been carrying out several rounds of private talks to forge a bi-lateral trade agreement.
The European Commission said its negotiators are accountable to the EU Member States in the Council and the European Parliament who will ultimately vote on TTIP. It said the negotiations' aim was:
The Commission said the decision to start negotiations was mainly due to the "continuing economic crisis and the stalling of the multilateral trade negotiations in the World Trade Organisation" along with changes in the EU's agriculture policy.
But those opposed to TTIP are urging MEPs to vote against the deal when it reaches the European Parliament.
One of the more contentious parts of the negotiations concerns the Investor State Dispute Settlements (ISDS), which would allow companies to sue governments if state-enforced policies prevent their ability to turn a profit.
In Britain, the protests' chief focus is on the impact TTIP would have on the NHS, with claims it would enforce privatisation by the back door.
Health Secretary Jeremy Hunt has insisted there is no threat to the NHS from the agreement, which the Prime Minister believes could be worth £10bn to the UK economy.
If it succeeds in the face of strong public opposition, TTIP will be the largest bilateral trade deal ever agreed.