AbstractThree processes by which tropocollagen units associate to yield highly specific aggregates have been examined. From the temperature coefficients of the amounts aggregated it is concluded that the complex “native” aggregation is endothermic, whereas both end‐to‐end and lateral aggregation are exothermic. These results combined with additional information lead to the conclusion that “native” aggregation is an entropy‐driven process in which hydrophobic bonding plays the dominant role. In contrast the reactions producing the lateral aggregate and the aggregate in which end‐to‐end bonding is dominant are electrostatically governed.