Weight loss programs can be broadly placed into two categories: Clinical programs and Non-clinical programs. Clinical programs are those conducted in a medical center, doctor's office or clinic. Non-clinical programs are "do it yourself" programs of various types that may or may not include regular group meetings.
A good explanation of the pros and cons of the two types of weight loss programs is provided at http://goldiesgirl.tripod.com/index.html. This blog also contains other useful information -- including the USDA food pyramid that most of us have committed to memory.