Many countries grant citizenship to the descendants of their nationals, on the principle of jus sanguinis ('right of blood'). Italy, Ireland, Poland, Germany, and others have well-known programs that can extend a passport to people who've never lived there, provided they can document the bloodline.
Eligibility depends on which ancestor, which generation, and whether the line was broken by emigration or naturalization elsewhere. It often requires gathering old birth, marriage, and naturalization records, but for those who qualify it can be the easiest route to a second passport.
Why it matters for your move
If you have recent ancestry from certain countries, citizenship by descent can hand you the right to live and work there — and often across a whole bloc like the EU — without a visa at all. It's worth checking before assuming you'd need one.