Background: The energy intake necessary to maintain weight and body composition is called the energy requirement for weight maintenance and can be determined by using the doubly labeled water (DLW) method. Objective: The objective was to determine the energy requirements of nonobese men and women in the Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy 2 study. Design: Energy requirements were determined for 217 healthy, weight-stable men and women [aged >21 to <50 y; 70% female, 77% white; body mass index (BMI; in kg/m2) 22 to <28; 52% overweight] over 28 d with 2 consecutive 14-d DLW assessments in addition to serial measures of body weight and fat-free mass and fat mass by dual-energy X-ray absorptiometry. Energy intake and physical activity were also estimated by self-report over ≥6 consecutive d in each DLW period. Results: Total daily energy expenditure (TDEE) was consistent between the 2 DLW studies (TDEE1: 2422 ± 404 kcal/d; TDEE2: 2465 ± 408 kcal/d; intraclass correlation coefficient = 0.90) with a mean TDEE of 2443 ± 397 kcal/d that was, on average, 20% (580 kcal/d) higher in men than in women (P < 0.0001). The regression equation relating mean TDEE to demographics and weight was as follows: TDEE (kcal/d) = 1279 + 18.3 (weight, kg) + 2.3 (age, y) - 338 (sex: 1 = female, 0 = male); R2 = 0.57. When body composition was included, TDEE (kcal/d) = 454 + 38.7 (fat-free mass, kg) - 5.4 (fat mass, kg) + 4.7 (age in y) + 103 (sex: 1 = female, 0 = male); R2 = 0.65. Individuals significantly underreported energy intake (350 kcal/d; 15%), and underreporting by overweight individuals (~400 kcal/d; 16%) was greater (P < 0.001) than that of normal-weight individuals (~270 kcal/d; 12%). Estimates of TDEE from a 7-d physical activity recall and measured resting metabolic rate also suggested that individuals significantly underreported physical activity (~400 kcal/d; 17%; P < 0.0001). Conclusion: These new equations derived over 1 mo during weight stability can be used to estimate the free-living caloric requirements of nonobese adults. This trial was registered at clinicaltrials.gov as NCT00427193.