TLDR: Inheritance rules change completely once you cross a border, and a will that works perfectly in one country can create real problems in another. If you own property, have family, or plan to retire outside your home country, you need to understand how these systems clash before you write your will, not after.
Why One Will Doesn't Always Work Everywhere
A lot of people assume a will is a will. Sign it, notarize it, done. But that's not how it works once you own a bank account in Spain, a rental property in Thailand, or you're a US citizen married to someone from France. Each country has its own rules about who gets what, and some of those rules don't care what your will says.
Take forced heirship. In France, Italy, and much of Latin America, a portion of your estate is legally reserved for your children no matter what your will states. You can't leave everything to a charity or a second spouse if it violates that reserved share. Compare that to the US or UK, where you generally have freedom to leave your assets to whoever you want, including nobody in your family at all.
Common Law vs Civil Law Systems
This split traces back to two different legal traditions. Common law countries, like the US, UK, Canada, and Australia, treat a will as an expression of personal choice. Civil law countries, like France, Germany, Japan, and most of Latin America, treat inheritance as something owed to close family by default.
If you're from a common law background and you buy a vacation home in a civil law country, your assumptions about "my property, my rules" might not hold up. Local law can override your will for that specific asset, even if your will is perfectly valid where you live.
What Happens When You Own Property in Multiple Countries
This is where things get messy fast. Say you're a US citizen with a house in California and an apartment in Portugal. Portugal may apply its own succession rules to the Portuguese property, regardless of what your California will says, unless you've specifically addressed it.
Some countries let you choose which nation's law applies to your estate through an EU regulation known as Brussels IV, which allows EU nationals and residents to elect their home country's inheritance law instead of the country where the property sits. That's a useful tool, but it only works if your will explicitly states the choice. Miss that step and the default local rules kick in.
Dual Wills and When They Make Sense
For people with assets in two or more countries, many estate lawyers recommend separate wills, one for each jurisdiction, carefully written so they don't accidentally cancel each other out. A poorly worded second will can revoke the first one entirely, which is the opposite of what anyone wants.
This isn't a DIY project. You need someone familiar with both legal systems checking the language, because a phrase that sounds harmless in English can have unintended legal weight somewhere else.
Inheritance Tax Varies Wildly Too
Even if the who-gets-what question gets settled, taxes are a separate fight. The UK charges inheritance tax at 40% above a certain threshold. The US has an estate tax that mostly affects large estates, currently exempting several million dollars per person. Some countries, like Australia and Canada, don't have an inheritance tax at all, though Canada taxes capital gains on death instead.
If your heirs live in a different country than you do, they might owe tax in their home country too, on top of whatever the estate already paid. Double taxation treaties exist between some nations to prevent this, but not all countries have one with each other.
Religious and Cultural Inheritance Rules
In several countries, inheritance law is tied directly to religious practice. Under Sharia-based systems used in parts of the Middle East and North Africa, inheritance shares for sons, daughters, spouses, and parents are fixed by religious law, and a will can only redirect a limited portion of the estate, often capped at one third.
Blending Personal Wishes With Legal Requirements
For families navigating these rules, especially mixed-nationality couples or expats, the goal usually becomes finding where personal wishes and legal requirements can meet. A good estate lawyer familiar with the relevant religious and civil frameworks can usually structure gifts, trusts, or lifetime transfers that respect both.
What to Actually Do About It
Start by listing every country where you hold property, citizenship, or residency. Then find out, country by country, whether forced heirship applies, whether you can elect foreign law under something like Brussels IV, and what the local inheritance tax looks like.
After that, talk to a lawyer who works across borders, not just one who's good in your home country. Cross-border estates aren't something to figure out after the fact. The paperwork is a lot cheaper than the legal fight your family could end up in without it.