Technical Abstract: This chapter outlines the known gender differences in fat gain, loss, and maintenance, and perhaps more importantly, highlights how little is known about the subject. The effects of gender differences on body fat distribution, fat use as an energy source, and exercise-related fat loss are discussed. Gender differences in fat distribution result from region-specific differences in fat accumulation and mobilization. Due to these differences, men tend to retain visceral and upper body fat, while women tend to store subcutaneous lower body fat. Due to a higher percentage of fat free mass, men have higher metabolic rates than women. Women burn more fat than men during exercise, but burn less at rest or in a fasted state. Although total calories consumed is important to body fat changes in both genders, macronutrient ratios may also be important in women. For women, dietary fat is positively associated with percent body fat, while dietary carbohydrate is negatively associated with body fat. Exercise alone seems to be an effective way of maintaining or reducing body fat in men, but not in women. In fact, total energy expenditure is positively associated with body fat percentage in women. Some scientists have suggested that women tend to compensate for exercise by consuming more calories, but this has not been proven. Overall, the data suggests that women gain and retain body fat more readily than men, independent of physical activity level.