Asceticism describes a life-style characterized by voluntary abstinence from various sorts of worldly pleasures (especially sexual activity, the consumption of alcohol and the accumulation of property and wealth), often with the aim of pursuing religious or spiritual goals.

In ancient Greek philosophy, the adherents of Cynicism and Stoicism adopted the practice of mastering desire and passion, as to some extent did Epicureanism. Diametrically opposed to Asceticism is Hedonism, the philosophy that pleasure is the most important pursuit of mankind.

The justification behind Asceticism is usually that spiritual and religious goals are impeded by indulgence in pleasures of the flesh, although it does not necessarily hold that the enjoyment of life is bad in itself. Thus, ascetic practices are not usually regarded as virtuous as such, merely a means towards a mind-body transformation, or a purification of the body which enables connection with the Divine and the cultivation of inner peace. It aims to achieve freedom from compulsions and temptations, bringing about peacefulness of mind and an increase in clarity and power of thought.

A distinction is sometimes drawn between "otherworldly" Asceticism (which is practiced by people, such as monks or hermits, who withdraw from the world in order to live an ascetic life) and "worldly" Asceticism (which refers to people, such as the Quaker and Amish sects, who live ascetic lives but do not withdraw from the world).

The term "asceticism" derives from the Greek "askesis" (meaning "practice", "training" or "exercise"), and it was originally associated with any form of disciplined practice. In ancient Greek society, warriors and athletes often applied the discipline of askesis to attain optimal bodily fitness and grace.

The founders and earliest practitioners of many religions (e.g. Hinduism, Jainism, Judaism, Christianity, Buddhism) lived extremely austere lifestyles, refraining from sensual pleasures and the accumulation of material wealth.

• Hindu Sadhus (or holy men) are known for the extreme forms of self-denial they occasionally practice, such as vowing never to use one leg or the other, or to hold an arm in the air for a period of months or years.
• Jainism encourages fasting, yoga practices, meditation in difficult postures, barefoot travel, and sleeping on the floor without blankets. Some have claimed to have gained magical or miraculous abilities through self-denial.
• The history of extreme Jewish Asceticism goes back thousands of years to the Wilderness Tradition that evolved out of the forty years in the desert, although today it is considered contrary to God's wishes for the world.
• Although certain Catholic orders (e.g. Carthusians, Cistercians) are known for especially strict acts of Asceticism, even more rigorous ascetic practices were common in the early Church, and the deserts of the Middle East were at one time said to have been inhabited by thousands of Christian hermits.
• Interestingly, Siddhartha Gautama (the Buddha), who initially counselled an ascetic life, eventually rejected extreme Asceticism as an impediment to ultimate freedom, recommending instead the "Middle Way".
• Although Asceticism is not an important tradition in Islam, apart from from in Sufism (which is even named for the rough woollen robe of the ascetic), the Prophet Muhammad himself practiced great austerities, verging on Asceticism.