Characteristics of gelatin are briefly described from the view point of a photographic binder, especially with regard to following items: 1. Development of photographic gelatin, 2. Collagen and its conversion to gelatin, 3. Size and conformation of the gelatin molecule, 4. Characteristic amio acid composition of gelatin and its relation to the physico-chemical bihavior of gelatin, especially as a polyampholyte.