Teetotalism is the practice of voluntarily abstaining from the consumption of alcohol. A person who practices (and possibly advocates) teetotalism is called a teetotaler (US) or teetotaller (UK), or said to be teetotal. Globally, in 2016, 57% of adults did not drink alcohol in the past 12 months, and 44.5% had never consumed alcohol. A number of temperance organizations have been founded in order to promote teetotalism and provide spaces for nondrinkers to socialise.

According to the Online Etymology Dictionary, the tee- in teetotal is the letter T, so it is actually t-total, though it was never spelled that way. The word is first recorded in 1832 in a general sense in an American source, and in 1833 in England in the context of abstinence. Since at first it was used in other contexts as an emphasised form of total, the tee- is presumably a reduplication of the first letter of total, much as contemporary idiom might say "total with a capital T".

The teetotalism movement first started in Preston, England, in the early 19th century. The Preston Temperance Society was founded in 1833 by Joseph Livesey, who was to become a leader of the temperance movement and the author of The Pledge: "We agree to abstain from all liquors of an intoxicating quality whether ale, porter, wine, or ardent spirits, except as medicine." Today, a number of temperance organisations exist that promote teetotalism as a virtue.

Richard Turner, a member of the Preston Temperance Society, is credited with using the existing slang word teetotally for abstinence from all intoxicating liquors. One anecdote describes a meeting of the society in 1833, at which Turner in giving a speech said, "I'll be reet down out-and-out t-t-total for ever and ever." Walter William Skeat noted that the Turner anecdote had been recorded by temperance advocate Joseph Livesey, and posited that the term may have been inspired by the teetotum; however, James B. Greenough stated that "nobody ever thought teetotum and teetotaler were etymologically connected."

A variation on the above account is found on the pages of The Charleston Observer:

Teetotalers.—The origin of this convenient word, (as convenient almost, although not so general in its application as loafer,) is, we imagine, known but to few who use it. It originated, as we learn from the Landmark, with a man named Turner, a member of the Preston Temperance Society, who, having an impediment of speech, in addressing a meeting remarked, that partial abstinence from intoxicating liquors would not do; they must insist upon tee-tee-(stammering) tee total abstinence. Hence total abstainers have been called teetotalers.

According to historian Daniel Walker Howe (What Hath God Wrought: The Transformation of America, 1815–1848, 2007) the term was derived from the practice of American preacher and temperance advocate Lyman Beecher. He would take names at his meetings of people who pledged alcoholic temperance and noted those who pledged total abstinence with a T. Such persons became known as Teetotallers.

When at drinking establishments, teetotallers tend to consume non-alcoholic beverages such as water, juice, tea, coffee, non-alcoholic soft drinks, virgin drinks, mocktails, and alcohol-free beer.