They are part of the EU and are part of the EU customs area, there is no practical difference with other EU territories regarding trade.

They are not part of Schengen (but EU citizens don't need any visa, it's mostly intended to curb illegal immigration from South America via Guiana) and have the ability to use different VAT rates from mainland France, but that's all.

Yes, but Martinique is not considered a territory, and is considered part of the EU.

French Guiana is in the EU.

Sure they are, 2 seconds of googling compared to a minute writing your post:

> The European Union (EU) has nine 'outermost regions' (ORs): Guadeloupe, French Guiana, Martinique, Mayotte, Réunion and Saint Martin (France), the Canary Islands (Spain) and the Azores and Madeira (Portugal). The ORs are an integral part of the EU and must apply its laws and obligations.

I found it interesting that when the UK was part of the EU, the Isle of Man was not, but because they held British Passports, the people of the Isle of Man were EU citizens.

> the people of the Isle of Man were EU citizens.

Not quite, at least not by default. The pre-Brexit Manx passport did confusingly include the text "European Union" on its cover, but holders of Manx nationality were only citizens of the EU if they had lived for at least 5 consecutive years in the UK or if they descended from a UK parent or grandparent.

Source: https://en.wikipedia.org/wiki/Isle_of_Man-variant_British_pa...

It's the same for all the non-EU French territories. EU citizenship is not territorial, it's directly linked to the person's nationality so you wouldn't remove EU citizenship from a French citizen just because he happens to live in New Caledonia. French or British citizens living in Canada also are EU citizens after all.

The state of British citizenship is a bit more complicated though I think. A bit like US citizenship which kinda depends on which US territory one lives, as far as I understand.

No, a British citizen is a British Citizen wherever you live. There are tax implications based on where you live, but that's unrelated.

Right, but citizens of British overseas territories, crown dependencies and whatever other statuses exist are not necessarily British citizens. Same as with the various US territories.

This is what I meant when I said these citizenships work in more complicated ways than the French one.

I think all French territories are part of the EU, but some other countries work differently. The prime example is St. Martin, where the French part is in the EU, but the Dutch isn't (yes that technically puts a EU border through the middle of the island, although there were no pass controls when I was last there.).