A revenue stamp, tax stamp, duty stamp or fiscal stamp is a (usually) adhesive label used to designate collected taxes or fees on documents, tobacco, alcoholic drinks, drugs and medicines, playing cards, hunting licenses, firearm registration, and many other things. Typically, businesses purchase the stamps from the government (thereby paying the tax), and attach them to taxed items as part of putting the items on sale, or in the case of documents, as part of filling out the form.

Revenue stamps often look very similar to postage stamps, and in some countries and time periods it has been possible to use postage stamps for revenue purposes, and vice versa. Some countries also issued dual-purpose postage and revenue stamps.

Revenue stamps are stamps used to designate collected taxes and fees. They are issued by governments, national and local, and by official bodies of various kinds. They take many forms and may be gummed and ungummed, perforated or imperforate, printed or embossed, and of any size. In many countries, they are as detailed in their design as banknotes; they are often made from the same type of paper. The high value of many revenue stamps means that they may contain security devices to prevent counterfeiting.

The Revenue Society has defined revenue stamps as " ...stamps, whether impressed, adhesive or otherwise, issued by or on behalf of International, National or Local Governments, their Licensees or Agents, and indicate that a tax, duty or fee has been paid or prepaid or that permission has been granted."

In the Ottoman Empire, Damga resmi was already in use by the sixteenth century. Records of tax revenue from stamps for silk provide evidence of changes in silk production over time.

The use of revenue stamps goes back further than that of postage stamps (first used in 1840); the stamps of the Stamp Acts of the 18th century were revenues. Their use became widespread in the 19th century, partly inspired by the success of the postage stamp, and partly motivated by the desire to streamline government operations, the presence of a revenue stamp being an indication that the item in question had already paid the necessary fees. Revenue stamps have become less commonly seen in the 21st century, with the rise of computerization and the ability to use numbers to track payments accurately.

There are many kinds of revenue stamps in the world, and it is likely that many remain unrecorded. Both national and local entities have issued them. Governments have sometimes combined the functions of postage and revenue stamps. In the former British Empire, such stamps were often inscribed "Postage and Revenue" to reflect their dual function. Other countries have simply allowed revenue stamps to be used for postage or vice versa. A revenue stamp authorized subsequently for postal use is known as a postal fiscal. Bhutan, for instance, authorized the use of revenue stamps for postal purposes from 1955 until the first proper postage stamps of the country were issued in 1962. In the Stanley Gibbons catalog, this type of stamp has an F prefix.

While revenue stamps often resemble postage stamps, they are not normally intended for use on mail and therefore do not receive a postal cancellation. Some countries such as Great Britain have issued stamps valid for both postage and revenue, but this practice is now rare. Many different methods have been used to cancel revenue stamps, including pen cancels, inked handstamps, perforating, embossing, hole punching or simply tearing.