My grandfather emigrated from portugal and settled in trinidad, west indies. How can I qualify for portuguese citizenship.

This might help...
http://www.acime.gov.pt/docs/Publicacoes/brochingl/Nacionalid.pdf.

My grandfather emigrated from portugal and settled in trinidad, west indies. how can i qualify for portuguese citizenship.

As granchild of a Portuguese citizen, you are eligible to apply for the Portuguese citizenship.

However, the procedure that you must follow will depend on whether your father/mother that is descendent of your grandfather is still alive.

There are also other aspects that would influence on the obtainment of the Portuguese citizenship, but then you would have to give me further details about your family in order to allow me to provide you accurate information about the procedures, necessary documents, applications , etc.

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