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Portugal — Exceptional Talent
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This is the lightest route into Portugal for anyone who has it, and on what you have told us you have it.
A researcher admitted by a recognised research centre or a higher education institution can obtain a residence visa on a hosting agreement or an employment contract, together with a grant, a funded position or the institution's undertaking to cover your stay. Researchers admitted by institutions approved under the scheme are expressly exempted from producing several of the documents the general rules require, including some of the means-of-subsistence evidence.
There is a shorter alternative for a stay of under a year: a temporary-stay visa for research or highly qualified activity, which avoids the residence-permit system entirely. And if the position is longer term, the residence route gives a permit valid two years and renewable for three.
What to ask your host institution: whether they are on the approved list, since it materially reduces the paperwork; whether the hosting agreement or contract is drafted to include the elements the law requires — the subject and duration of the research, and the institution's undertakings; and whether they will handle the EU mobility provisions if your project involves periods in other member states, which have their own notification rules.
The time counts as legal residence, so permanent residence arrives at five years with basic Portuguese, and naturalisation at seven years for nationals of Portuguese-speaking countries and of EU states, ten for everyone else.