How do you say Happy Anniversary in French?

If you want to wish a happy birthday : "Joyeux anniversaire", or "bon anniversaire".

If you're talking about a wedding birthday you can say : "Joyeux anniversaire de mariage", or "Bon anniversaire de mariage". You can also wish a happy wedding birthday by saying "Joyeuses noces de coton" if the couple has been married for one year, or "Joyeuses noces de diamant" if they've been married for 60 years. And each year of marriage has a different name, the longer it lasts, the more precious it gets. You can find all the names at the Related Link.