In the 21st century, those who practice yoga may do so to achieve enlightenment, or for a variety of other reasons to find peace of mind, to reduce the effects of stress on the body and the mind, to deal with physical pain or injury, or to become mentally or physically strong and flexible. Whatever the goal maybe, when Tapas are applied to the practice of yoga it becomes a powerful tool for transformation. Initially yoga was understood as a spiritual practice and the term Tapas was also used for the same purpose. In recent times, Tapas have also attained the implication of abstinence and self-disciple. The actual understanding of Tapas is fire and radiance. By the practice of Tapas, the inner self shines very bright through the physical body. Also, by practicing Tapas spiritual S¿dhakas radiate the energy of wisdom and kindness. Tapas is understood as subjecting the body to hardships so that it can endure heat, cold, poisons and so on. For meditation a strong body is required. Austerities that purify the body, thoughts and emotions and train the senses are required to be performed diligently. In various Indian religions Tapas refers to spiritual discipline. Jainism refers to austerity and self-denial, Buddhism refers to contemplation, self- discipline and in the various other societies among Hinduism it refers to various observances extending from austerity to purification to disciplining of the self. Tapas needs to be observed in seclusion and is a bit of austere observances that are accepted in the process to emancipation. This chapter presents various concepts of Tapas and its evolution as austerities in different religions. The austerities of countless varieties are described in different religions, and the practitioner has the option to choose any practice regularly as per one's own liking.