Obesity is not just a disease of developed nations. Obesity levels in some lower-income and transitional countries are as high as or higher than those reported for the United States and other developed countries, and those levels are increasing rapidly. Shifts in diet and activity are consistent with these changes, but little systematic work has been done to understand all the factors contributing to these high levels. The goal of this review is to provide an understanding of the patterns and trends of obesity around the world and some of the major forces affecting these trends. Several nationally representative and nationwide surveys are discussed.