Dragonriders of Pern

This is set on another planet called Pern. For 50 years every 200 years Thread falls from the sky at regular intervals. Thread burns and destroys everything living that it touches, very not good. To protect themselves from the thread, the original settlers bred Dragons to fly and destroy the threads. These three books take place after a 400 year interval of no Thread. Everyone believes that Thread is gone permanently and because of this dragons and their riders are viewed as parasites on humanity and there are hardly any dragons left. Go figure, thread starts falling again and they aren't prepared, but F'lar and Lessa come up with ways of dealing with the situation.

In the first book, F'lar finds Lessa and eventually they become Weyrwoman and Weyrleader, and it's up to them to convince people that thread is coming and that people need to be prepared for it. After thread starts falling, the two of them realize that they are horribly unprepared for it, so Lessa jumps back in time 400 years to get more dragons to help fight thread. Yay!

In the second book, Thread starts falling randomly instead of regularly and it causes major stress. The oldtimers that came forward in time in the last book aren't adjusting well to the times and manage to get themselves banished to the southern continent.

The third book is focused on the White Dragon who was impressed by Jaxom who is the Lord Holder of Ruatha Hold. His dragon is much smaller than the other dragons, the wrong color, and he can't be a real dragonrider because he has to be a Lord Holder. It's a very difficult situation for the poor boy.

I love these books and I think I'm going to track down the rest of them.