2 Potato is a highly versatile crop grown in varying environmental conditions viz. plains, hills, and plateau in India. It is grown under short days in the plains in autumn season and under long days during summers in hills. Therefore, the pattern of growth, duration of crop as well as the yield varies according to the environment. Besides, the potato cultivars differ from each other in relation to their morphological characters, response to the environmental factors and finally in yield and the dry matter accumulation. The present chapter deals with the physiological factors, which determine the growth, development and finally the yield of potato crop.