The excellent Access to Archival Databases facility has a vast number of subjects. By no means all of them are directly relevant to genealogical research, but a fair few are. Here are the best examples, but there are others – and it’s worth keeping an eye on the list from time to time to see what else is being added:

• Germans to America Passenger Data File, 1850-1897
• Famine Irish Passenger Record Data File, 1846-1851
• Italians to America Passenger Data File, 1855-1900
• Russians to America Passenger Data File, 1834 – 1897

(NB Poland was divided between the German, Russian and Austrian Empires in the 19th century, so if you have Polish ancestors who emigrated during that time you may well find themin the German or Russian records.)

You can find out more at the US National Archives Access to Archival Databases home page:
http://aad.archives.gov/aad/

Poland was wiped off the map as an independent country at the end of the 18th century, and didn’t reappear until after the First World War – and then had its frontiers drastically redrawn westwards in 1945. So present-day Poland was once divided between two German kingdoms, the Austrian Empire, the Kingdom of Hungary and the Russian Empire; while parts of inter-war Poland are now in Lithuania, Belarus, Ukraine and the Czech Republic!

However, there’s a handy website that gives you a few useful hints on how to make progress in your search for your Polish ancestors. PolishRoots.org has several informative and helpful pages covering the redrawing of Poland’s frontiers between the 19th century and the present day. You can also get information on how local government and record-keeping under the various administrations in Poland were organised, how to identify changing Polish surnames, and how to apply for certificates of birth, marriage and death as well as records from the various religious communities – Catholic, Lutheran and Jewish. There’s even a potted history of Poland from the mid-18th century onwards.

All this can be found by following this link:
http://www.polishroots.org/genpoland/