The WTO was created in 1995 by the Uruguay Round agreements. Formerly, international trade (in goods only) was regulated by the General Agreement on Tariffs and Trade (GATT) and an organization also known as GATT. GATT was incorporated into the much larger WTO, which regulates international trade in goods, services and intellectual property.
The WTO Web site posts the Uruguay Round agreements and many of other documents, plus other publications and information.
WTO ministerial declarations are available on Westlaw (WTO-DEC). WTO Dispute Settlement Reports are on Lexis (ITRADE;WTODS).
A bibliography of materials published by the WTO is available in Introduction to International Business Law: Legal Transactions in a Global Economy (Chapter 10). For more information and resources, see Jeanne Rehberg's WTO and GATT Research.