This is often seen on lists of must-read fantasies, but it's really science-fiction (albeit with a fantasy feel). Pern is a lost colony of Earth. Dragons were bread from a species native to that planet--and are the natural enemy of the "spores" that periodically cause havoc. This is an influential book--you can see the similarities in other books, not just ones also featuring dragons, but ones that also feature close human/creature bonds, such as Lackey's novels featuring horse-like companions. Lessa is a strong and memorable heroine, and other characters in this book are just as appealing (particularly the Masterharper Robinton). This is one of those books that was in my permanent library until it literally fell apart in repeated readings. I do think at a certain point the series (there are about 20 books) lost its verve, even before her son began writing many of them, and I no longer pick up the new ones--but certainly the first three in the Dragonriders of Pern and Harper Hall series are enchanting and come to a satisfying resolution even if you don't hunt up more.