Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 161.In this book, we describe our current state of knowledge on circulation in the Gulf of Mexico through 22 papers at the forefront of research. The view is selective rather than all-inclusive, with primary focus on circulation at the sea surface and at depth, including nearshore flow. In choosing topics, we have attempted to avoid the distinction between observations and models, as both are essential to advance our understanding of this exceptional body of water. We have also written for specialists and non-specialists alike in both science and industry: for those who work directly on the science associated with the Gulf, and for those whose work depends on the Gulf. And we refer here to physical oceanography, marine geology, sedimentology, coastal and estuarine science, as well as to the petrochemical and fishing industries.