You can obtain a copy of the NAFTA text at the following web sites:
You can obtain a copy of the precursor to the NAFTA (i.e. the Canada - United States Free Trade Agreement) here:
The following versions of the NAFTA negotiating texts were finally made public by the three NAFTA governments in July 2004, after years of denying that they even existed, followed by a few more years of simply denying access. Two tribunals have already issued orders suggesting that more documents exist which could add to our understanding of the negotiations, but these contemporaneous texts are a decent start:
Canada and the United States of America have both recently revamped their respective model investment treaties. Explicitly borne out of their experience with NAFTA Chapter 11 dispute settlement
Three draft investment chapters can also be found here, excerpted from recent free trade agreements negotiated by the USA:
Two other types of documents are listed here: statements of the NAFTA Free Trade Commission and domestic implementation pronouncements (both of which have some international law interpretative value).
The Commission is essentially the official name used to describe whenever the three trade ministers from each NAFTA country meet to perform a function designated under the NAFTA. For the purposes of NAFTA Chapter 11, the NAFTA Commission is important because it can issue binding "interpretations" of NAFTA provisions, pursuant to Article 1131(2), which sets out the governing law for a Chapter 11 arbitration. In theory, if all three trade ministers agree that a NAFTA provision should be interpreted in a certain way, tribunals must obey them - no matter how far that interpretation may stray from the appropriate meaning of the text which would otherwise govern.
However, it is not clear if the three trade ministers can actually use this power as a sort of "sore loser" clause, ordering tribunals to "interpret" NAFTA provisions in a way that even previous tribunals have already concluded should not be done. The Commission's first statements (recorded immediately below) raised such concerns, but its later statements (made two years later and recorded further below) suggest that the NAFTA Parties may also see the Commission as a general clearinghouse for joint-statements on the operation of the Chapter, in that they are now issuing mere "recommendations" which clearly could not be binding under NAFTA Article 1131(2).
When the United States and Canada implemented the NAFTA through their domestic legislative processes, each provided a document which briefly described the obligations they had just undertaken. While these documents do not necessarily have any weight in the interpretation of the NAFTA’s provisions, they can nonetheless be instructive.