Between October 16th and 26th of 1973, Washington D.C. held the Diplomatic Convention on Wills to discuss providing a uniform law on the structuring of an International Will. Following three previous conventions – the Hague Convention of October 1st, 1973, the Hague Convention of October 5th, 1961, and the Convention on the Establishment of a Scheme of Registration of Wills in Basel on May 16, 1972 – the Washington Convention strove to agree on a certain form of Will acceptable to the internal law of every country and qualifying jurisdiction.

Organized by the International Institute for the Unification of Private Law (UNIDROIT) and signed or ratified by 20 countries, the Convention providing a Uniform Law on the Form of an International Will (is referred to as the International Wills Treaty, Uniform Wills Recognition Act or the UNIDROIT Wills Treaty) entered into force on February 9th, 1978. For ease of reference, we use the term “Treaty” in this blog.



The states and countries adopting the Treaty agree to recognize the validity of Wills executed in other states or countries that have adopted the Treaty as well, provided that the Will complies with the requirements of the Treaty.

The Treaty is broken down into 16 articles – which entails the process that the contracting parties (the countries and states) need to undertake – and an Annexure with 15 articles – which describes the requirements of an international will for it to be compliant (the Annex becomes the Uniform Wills Recognition Act). To read more about the requirements of an international will, read our blog “Should you have an “International Will”?”.


The United States

The United States, due to its federal nature, requires each individual state to ratify the Treaty and adopt the Annex into their State Codes. Although the US as a whole has signed the Convention and acts as the Depositary Government (to which the Treaty is entrusted under international law), less than half of the US States have ratified the Treaty or adopted the Annex as law.

We are the only multi-disciplinary international CPA firm in the United States that specializes in U.S.– Australia taxation.

Below is a list (derived from and cross-referenced with multiple US State codes as of 10/20/2020) of all of the US States, Districts, and Territories that have ratified the Treaty and adopted the Annex:

  1. Alaska
  2. California
  3. Colorado
  4. Connecticut
  5. Delaware
  6. Hawaii
  7. Illinois
  8. Maryland
  9. Michigan
  10. Minnesota
  11. Montana
  12. Nevada
  13. New Hampshire
  14. New Mexico
  15. North Dakota
  16. Oklahoma
  17. Oregon
  18. Vermont
  19. Virginia
  20. Wisconsin

+ the Virgin Islands

+ the District of Columbia

*the act has been introduced in Nebraska but has yet to be adopted



Since the Treaty aims to resolve the need for multiple Wills to cover international assets, it serves to provide testators with assets in the contracting jurisdictions to require only one “International Will” to cover these assets, provided that the Treaty guidelines are strictly adhered to. 

For example, if Jenna lives in California and has assets in Australia and in the UK, Jenna can opt to have a single “International Will” that covers all of her assets, as all three jurisdictions have ratified the Treaty.

On the other hand, if Jenna has assets in Alabama, Australia, the UK, and Spain, she may require multiple wills. As Alabama and Spain are not signatories to the Treaty and have not ratified the Treaty, depending on the nature and value of the assets in each of jurisdictions (and the consequent issues that could arise with obtaining probate in each such jurisdiction), Jenna may require separate Wills for Alabama and Spain, and could also have one international Will for her Australian and UK assets.

International estate planning is complex and you should always have a professional analysis of your assets undertaken to ensure that you Will is appropriately structured. Our whitepaper International Estate Planning for US-Australia cross-border clients provides an in-depth analysis of common international estate planning issues.


For more information on cross-border structuring of assets and Wills, please contact:

Renuka Somers
Head, US-Australia Tax Desk

Prerna Polepally
Intern, US-Australia Tax Desk