Tax residency is the gateway status of personal international tax: residents are typically taxed on worldwide income, non-residents only on local-source income. Every country defines it by its own domestic tests (Türkiye: domicile or six-plus months’ presence; Spain: 183 days or center of economic interests), so it’s possible to be resident in two places at once — which is what treaty tiebreaker rules exist to resolve.
Tax residency
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