A holographic will, or olographic testament, is a will and testament which is a holographic document, for example, it has been entirely handwritten and signed by the testator. Traditionally, a will had to be signed by witnesses attesting to the validity of the testator's signature and intent, but in many jurisdictions, holographic wills that have not been witnessed are treated equally to witnessed wills and need only to meet minimal requirements in order to be probated:

There must be evidence that the testator actually created the will, which can be proved through the use of witnesses, handwriting experts, or other methods.

The testator must have had the intellectual capacity to write the will, although there is a presumption that a testator had such capacity unless there is evidence to the contrary.

 The testator must be expressing a wish to direct the distribution of his or her estate to beneficiaries.

Holographic wills are common and are also often created in emergency situations, such as when the testator is alone, trapped, and near death. Jurisdictions that do not generally recognize unwitnessed holographic wills may grant exceptions to members of the armed services who are involved in armed conflicts and sailors at sea, though in both cases the validity of the holographic will expires at a certain time after it is drafted.

Holographic wills often show that the requirements for making a valid will are minimal. The Guinness Book of World Records lists the shortest will in the world as "Vše ženě" (Czech), "everything to wife"), written on the bedroom wall of a man who realized his imminent death. It clearly meets the minimum requirements, being his own work and no one else's. On 8 June 1948 in Saskatchewan, Canada, a farmer named Cecil George Harris who had become trapped under his own tractor carved a will into the tractor's fender. It read, "In case I die in this mess I leave all to the wife. Cecil Geo. Harris." The fender was probated and stood as his will. The fender is currently on display at the law library of the University of Saskatchewan College of Law.

In the U.S. State of Arizona, the postscript to a letter was upheld as a valid holographic will.