In the past, you might never know if you were duplicating some other genealogist's research. Today, thanks to CD-ROMs and the Internet, it's possible to share discoveries and even to download whole sections of your family tree. Enormous pedigree databases made up of family files from thousands of genealogists around the world make it easier than ever before to collaborate with other researchers and benefit from their findings. Your family tree can grow by dozens, even hundreds of names with just a few clicks — if you know where to look.

Here we look at 10 pedigree databases containing nearly 285 million names — among them, perhaps, some of your ancestors. Information in these files typically includes not only names, but also dates and places of birth, marriage and death, and sometimes biographical sketches and even pictures. Individuals are linked together in families so, once you make a connection, you can instantly extend your pedigree back several generations. You'll also find the name and address of the submitter, who may be able to provide additional details.