In the XXth century, some of the emerging environmental agreements were designed to include powerful economic incentives. At the same time, environmental commitments started to enter treaties on trade. This led to the potential for a conflict between environmental measures limiting trade and GATT/WTO norms protecting the free market. Besides, the emerging environmental crisis triggered the debate about incorporation of environmental values at the WTO level. The issues were a subject of discussion at GATT/WTO for decades. Meanwhile, regional trade arrangements prepared a platform for obligations under environmental treaties to be compatible with free trade. These arrangements are examined as legal instruments suitable to reconcile both trade and environmental values.