The weekdays and weekend are the complementary parts of the week devoted to labour and rest, respectively. The legal weekdays (British English), or workweek (American English), is the part of the seven-day week devoted to working. In most of the world, the workweek is from Monday to Friday and the weekend is Saturday and Sunday. A weekday or workday is any day of the working week. Other institutions often follow this pattern, such as places of education. The constituted weekend has varying definitions, based on determined calendar days, designated period of time, and/or regional definition of the working week (e.g., commencing after 5:00 p.m. on Friday and lasting until 6:00 p.m. on Sunday). Sometimes the term "weekend" is expanded to include the time after work hours on the last workday of the week (e.g., Friday evening is often referred to as the start of the weekend).

In some Christian traditions, Sunday is the "day of rest and worship". The Jewish Shabbat or Biblical Sabbath lasts from sunset on Friday to the fall of full darkness on Saturday; as a result, the weekend in Israel is observed on Friday–Saturday. Some Muslim-majority countries historically instituted a Thursday–Friday weekend. Today, many of these countries, in the interests of furthering business trade and cooperation, have shifted to Friday–Saturday or Saturday–Sunday as in the case of Saudi Arabia and UAE.

The Christian Sabbath is just one day each week, but the preceding day (the Jewish Sabbath) came to be taken as a holiday as well in the 20th century. This shift has been accompanied by a reduction in the total number of hours worked per week. The present-day concept of the "weekend" first arose in the industrial north of Britain in the early 19th century. The Amalgamated Clothing Workers of America union was the first to successfully demand a five-day work week in 1929.

Some countries have adopted a one-day weekend, i.e. either Sunday only (in seven countries), Friday only (in Djibouti and Somalia), or Saturday only (in Nepal). However, most countries have adopted a two-day weekend, whose days differ according to religious tradition, i.e. either Friday and Saturday, or Saturday and Sunday, or Friday and Sunday (in Brunei Darussalam, Aceh province (Indonesia) and state of Sarawak (Malaysia)), with the previous evening post-work often considered part of the weekend. Proposals continue to be put forward to reduce the number of days or hours worked per week, on the basis of predicted social and economic benefits.