Ayurveda, being an eternal science of human life deals with physical, psychological, spiritual well being of an individual. All the living organisms always hunted for gaining, grabbing and preserving the bala (vitality & strength) to enjoy the same for long period. Bala is the strength of body which expresses itself with great physical strength and stable psychological status with fully immune body to resist against the demerits of continuously changing external environment. The bala is under the influence of kala (Seasons) which tends it to fluctuate. Efforts have been made to justify the affinity of bala & kala. The conceptual study bala is detailed with its associated parameter ojas, vyadhikshamatva along with kala particularly with visarga kala and ritu (seasons). An effort has been made to review the bala, functions, Classification & definition along with its compatible modern review. I hope this book will be beneficial for the teachers, upcoming students & research scholars of Ayurveda.