I live in Switzerland together with my partner (we are not married, do not have kids). We both have permit B. She has never worked in Switzerland and does not own any properties here. She holds one of EU countries passport and she owns properties as well has income there. According to Swiss tax system I am treated as single person in Switzerland and my employer is taking care of my tax at source accordingly. My question is if she has to prepare any tax return form in that case.

All Swiss residents are taxed on global assets and global income. She must file a tax return and declare all properties and revenues.

But with most (all?) EU countries, there is a double taxation agreement. However, when I had property abroad, my accountant asked me if, when it was sold, I'd bring the money into a Swiss account. If not, he would forget to include it on the tax return...

And before anyone gets on their high horse, ALL my assets have been declared. In fact, from the sale of house, I made a profit, which in the UK wasn't taxed, but in CH, when I put that profit as a tax-deductable deposit into my pension, gave me a very nice deduction on my income...

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First step is to submit the tax return and declare all assets and revenues. Depending on the pertinent tax treaty, assets and income taxed elsewhere may be partially or completely exempt from Swiss taxes.

Might be simpler to ask the tax office. Usually they are not interested in getting tax forms from "foreign" residents for outside Switzerland income unless the amounts are substantial.

Many thanks for all replays. Sorry, I did not mentined before that my partner is less then 50% of time in Switzerland per year. Does it make any difference?