To date, there have been very few studies on the primary prevention of obesity and/or weight gain. This paper identifies three times periods that might be appropriate for such efforts at weight gain prevention--the 25 to 35 year age window, the perimenopausal period, and the year following successful weight loss. Research is encouraged that compares these three time periods and various intervention strategies. Several different approaches to primary prevention are identified, including group treatment programs with weekly meetings vs. less intensive, community-based interventions; focusing on those who are currently at ideal body weight vs. including those who are overweight as well; and targeting weight gain prevention per se vs. attempting to produce modest weight losses and/or modify cardiovascular risk factors. This paper suggests that primary prevention efforts should include exercise, changes in quality and quantity of food consumed, behavior modification, and some degree of therapist contact, but the manner in which these changes should be implemented to produce long-term habit change remains unclear.