Can I claim Polish citizenship if my grandparent was Polish?

“Often, yes — Polish citizenship can pass down an unbroken line from a Polish parent, grandparent or great-grandparent, and is confirmed rather than granted. Whether your particular line qualifies is a legal question involving the 1920–1951 citizenship rules and the unbroken-descent requirement, for your adviser and the Polish authority. Whatever the outcome, the foreign documents must be sworn-translated into Polish.”