A vow of silence is a personal pledge to refrain from speaking. There are numerous reasons to take a vow of silence, with many people associating this concept with expressions of religious faith. Christians and Buddhists often incorporate vows of silence into their religious practice, for example, although one need not necessarily be religious to take a vow of silence.

Vows of silence have been a part of religious practice for centuries. The precise details of the vow vary, depending on the person and the circumstances. Some people take permanent vows of silence, in which they pledge never to speak. Others pledge to refrain from speech for a set period of time, such as a year, while others vow to remain silent until something is achieved. A vow of silence may also specify silence at particular times of the day. Many monasteries and cloisters have vows of silence which discourage speaking except during set times, for example.

In some regions, cloistered people take vows of Greater and Lesser Silence. The Greater Silence usually stretches from the last prayers in the evening to the morning prayers, and people may not speak at all during this period. In the Lesser Silence, which lasts from morning to evening prayers, people may speak to pray, and sometimes to convey critical information, but unnecessary conversation is not welcomed.

When someone takes a vow of silence, it is often with the intent of promoting religious contemplation. Some people feel that by ceasing to speak, they force themselves to focus inward, to think about the nature of faith and their own personal beliefs. A vow of silence also strips away the distractions of speech, which is why some residential religious communities use vows of silence, with the goal of encouraging people to ponder spiritual matters.

Someone may also take a vow of silence as an act of penance. Many people value the ability to speak, and giving up one's voice can be a potent symbolic act of penance. Other people sacrifice their voices to religious faith, much as religious ascetics give up luxuries of the world or the possibility of marriage. Some may use the vow of silence as an act of protest, pledging not to speak until demands are met. This form of the vow of silence is often seen in the “silent treatment” used by young children to punish each other for perceived wrongdoings, or to convey extreme displeasure to parents and other authority figures.