A tithe ( /ˈtaɪð/; from Old English: teogoþa "tenth") is a one-tenth part of something, paid as a contribution to a religious organization or compulsory tax to government. Today, tithes (or tithing) are normally voluntary and paid in cash, cheques, or stocks, whereas historically tithes were required and paid in kind, such as agricultural products (that grown of the land, or fruit of the tree). Several European countries operate a formal process linked to the tax system allowing some churches to assess tithes.

"Tithing" also has unrelated economic and juridical senses, dating back to the Early Middle Ages. See "Tithing (country subdivision)".

Traditional Jewish law and practice has included various forms of tithing since ancient times. Traditional Jews commonly practice ma'aser kesafim (tithing 10% of their income to charity) and take challah. In modern Israel, Jews continue to follow the laws of agricultural tithing, e.g., terumah, ma'aser rishon, terumat ma'aser, and ma'aser sheni. In Christianity, some interpretations of Biblical teachings conclude that although tithing was practiced extensively in the Old Testament, it was never practiced or taught within the first-century Church. Instead the New Testament scriptures are seen as teaching the concept of "freewill offerings" as a means of supporting the church: 1 Corinthians 16:2, 2 Corinthians 9:7. Also, some of the earliest groups sold everything they had and held the proceeds in common to be used for the furtherance of the Gospel: Acts 2:44-47, Acts 4:34-35. Further, Acts 5:1-20 contains the account of a man and wife (Ananias and Sapphira) who were living in one of these groups. They sold a piece of property and donated only part of the selling price to the church but claimed to have given the whole amount and immediately fell down and died when confronted by the apostle Peter over their dishonesty.