The book is based on Mason graduate course CLIM 752 Ocean General Circulation. Klinger also teaches an introductory course, CLIM 412/512 Physical Oceanography. While ocean currents are changing all the time, there is an underlying pattern of permanent current systems which can be found in all the oceans. These patterns have been uncovered by millions of oceanographic measurements from ships, buoys, and satellites, and can be explained from physical principles. The circulation affects not only the oceans themselves but also the global climate, because currents redistribute heat and other properties across the globe, changing atmospheric temperature and circulation. The book explores each circulation structure, demonstrating where in the ocean it can be found and explaining what determines its behavior.