EU leaders agreed on the treaty's outlines last month
The step, taken by EU foreign ministers in Brussels, aims to end two years of confusion after French and Dutch voters rejected a draft EU constitution.
Correspondents say there is a common desire to proceed quickly, turning the outlines of treaty agreed at a summit in June into a finished product.
The foreign ministers are also drawing up plans to send peacekeepers to Chad.
145-page draft
Portugal, which holds the EU presidency, submitted a first draft of 145 pages - plus 132 pages of protocols and declarations - to representatives of all member states at a short, low-key ceremony.
This marks the start of an intergovernmental conference (IGC), which is expected to thrash out a final text by a summit in Lisbon in October.
JUNE EU DEAL: MAIN ISSUES Double majority voting delayed until 2014 Long-term EU president High Representative for foreign affairs Fewer national veto powers More powers for the European Parliament
Son-of-constitution is born Q&A;: Reform treaty
Legal experts will begin going through the text in detail on Tuesday.
Poland's Foreign Minister Anna Fotyga made clear that the deal was not done yet.
"There are several issues many countries have and we would like to clarify them. The IGC is exactly for this," she said.
She signalled that Poland was no longer insisting on renewing discussions on the length of time EU legislation could be delayed, when countries opposing it have been narrowly outvoted.
However, she said Poland wanted the rules on this delaying procedure written into the text of the new treaty itself, instead of being included in a protocol, as planned.
Charter worry
Ms Fotyga also said Poland reserved the right to join the UK in opting-out of the Charter of Fundamental Rights.
"They are still looking to destroy the charter, practically speaking," said British Liberal MEP Andrew Duff.
"If this infection spreads, that will mean the end of the charter."
UK shadow foreign secretary William Hague is set to reiterate the Conservative Party's call for a referendum on the new treaty in a lecture in London on Tuesday.
But Europe Minister Jim Murphy said the UK government had no plans to hold a referendum.
He said that the only other country that was considering holding one was Ireland, and that was only because of its "particular constitutional arrangements".
Looking to the world outside, EU foreign ministers instructed their military planners to prepare a peacekeeping operation to protect tens of thousands of refugees from Darfur on the Chad border.
Strongly backed by France and Britain, the mission would include at least 1,500 troops and last up to a year.
Lisbon is to give its name to the latest EU treaty
European Union foreign ministers today opened an Intergovernmental Conference (IGC) beginning work on on a new treaty for the 27-member bloc. Portugal, the presiding country of the Union during the negotiations, presented its first draft of the 145 page document (with an extra 132 pages of protocols) to foreign ministers in a short ceremony opening the conference.

A mandate for the new Reform Treaty was agreed last month after drawn out European Council negotiations in Brussels. Under the German Presidency of the Union, leaders agreed to drop the proposed Constitution and its state-like elements, yet retain many of its institutional reforms: described by Angela Merkel (German Chancellor and then-Council President) in the terms ''“The fundamentals of the Constitution have been maintained in large part … We have renounced everything that makes people think of a state, like the flag and the national anthem.”'' This mandate is now going to be taken by the IGC, composed of national and European government officials, and converted into a legal text.

Negotiations are expected to go smoothly. Poland had originally intended to kick up a storm over the chosen voting system, as it stood to lose from the proposed QMV system and favoured keeping the old system or using an alternative. The negotiations concluded that the implementation of the new system would be delayed until 2014. Poland also claimed it had secured a Gentlemen's agreement that it could veto decisions for a further two years, but this was denied by other members. Isolated, Poland relented and agreed to back official agreement, with a minister stating: "Our priority is not to block decisions - we're interested in easier decision-making because we want the Union to function properly." The Polish Prime Minister stated that despite some opposition in Poland, there is no threat to governments' ability to ratify the document.

The IGC should conclude in Lisbon during October of this year and would shortly after be signed in the city; therefore, the city will give its name to the treaty. This will allow ratification throughout 2008 so it can come into force before the 2009 European elections. Most national ratification is expected to take place without referenda, to avoid a repeat of the "no" votes that halted the European Constitution.