A tithe (; 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 are normally voluntary and paid in cash or cheques or more recently via online giving, whereas historically tithes were required and paid in kind, such as agricultural produce. After the separation of church and state, church tax linked to the tax system are instead used in many countries to support their national church. Donations to the church beyond what is owed in the tithe, or by those attending a congregation who are not members or adherents, are known as offerings, and often are designated for specific purposes such as a building program, debt retirement, or mission work.

Many Christian denominations hold Jesus taught that tithing must be done in conjunction with a deep concern for "justice, mercy and faithfulness" (cf. Matthew 23:23). Tithing was taught at early Christian church councils, including the Council of Tours in 567, as well as the Third Council of Mâcon in 585. Tithing remains an important doctrine in many Christian denominations, such as the Congregationalist Churches, Methodist Churches and Seventh-day Adventist Church. Some Christian Churches, such as those in the Methodist tradition, teach the concept of Storehouse Tithing, which emphasizes that tithes must be prioritized and given to the local church, before offerings can be made to apostolates or charities.

Traditional Jewish law and practice has included various forms of tithing since ancient times. Orthodox Jews commonly practice ma'aser kesafim (tithing 10% of their income to charity). In modern Israel, some religious Jews continue to follow the laws of agricultural tithing, e.g., ma'aser rishon, terumat ma'aser, and ma'aser sheni.