Anne McCaffrey's best book: Dragonflight. This one makes my personal "top ten" list, and I highly recommend it. While this reads nicely as an episodic novel, it is a fix-up of a novella ("Weyr Search" - Analog October 1967), plus a short novel (Parts 3 and 4: "Dust Fall" + "The Cold Between" as "Dragonrider" - Analog December 1967 and January 1968), with an original novelet in-between. (I wonder if McCaffrey submitted that part ("Dragonflight") to Campbell and he rejected it for sexual content?) "Weyr Search" tied as winner of the Hugo Award for best novella in 1968 and was a Nebula-nominee in 1967. "Dragonrider" won the 1968 Nebula for best novella and was a Hugo-nominee in 1969. I'm guessing that the recent wins of the parts of the novel kept the combined version from showing up on the "best novel" nominations.

[I read my copy often and like it a lot, but for a better plot set-up than the back cover, I'm quoting the flap-copy from a hardcover reprint, which expands on the first-page blurb of this edition]:
For millenia the magnificent Dragons of Pern had given themselves in proud service to mankind. And the men who rode them were a breed apart, with special telepathic powers developed through long centuries to unite them with the dragons in defending the planet from the dreaded silver Threads that periodically floated gently down from space. The Dragonmen, no less than the glorious beasts they rode through the skies, were the elite of Pern, proud inheritors of the right and duty to defend their planet. But it had been long since Pern had needed any defense and the memories of tithe-payers and traditionalists alike were short. The Dragonweyr was shabby, its resources were meager, and, worst of all, the complement of fighting dragons had reduced itself to a handful of squadrons, pitifully inadequate to defend a whole planet if the Threads came. And they would...
There was need for a new Weyrwoman, of legendary stature. Only such a one could stir the Dragonmen into action, could repopulate the deserted weyrs, and return the forgetful populace to their allegiance. But where could such a one be found in these decadent days? It was only nostalgia that took the Dragonmen to Ruatha on their Search. The great line of Ruatha had been destroyed, and grass grew on the battlements of the Hold. But the dragons were restless. Somewhere in Ruatha there was power...