Quantification of behavior starts with the observation of behavioral phenomena. These observations can be classified by fundamental types of behavior and the energies associated with these behaviors can be measured or calculated using known procedures. Behaviors can occur, if, and only if, energy is available for use in the behavior and the behaving system has the capacity to direct energy. A relationship is developed among behavior, available energy, and the capacity to direct energy that gives a coherent interpretation of behavioral phenomena and allows the quantification of behavior.