This assessment is a summary of the accumulated scientific understanding of the estuary and Gulf of St. Lawrence. It discusses the extent of anthropogenic modifications to this marine environment, points out principal uncertainties that hinder our understanding, and identifies important regional environmental issues. Many assessments attempt to provide easy-to-understand information to a wide, non-specialist audience. Others are directed more specifically to scientists, but include a conclusions section written for non-scientists. This document offers something of a middle approach: it is intended to be understood by a non-specialist audience, albeit one with a general knowledge of contemporary science. At the same time, it gives the professional scientist a broad-scale synthesis of current information.