Worlds of Exile and Illusion by Ursula K. LeGuin
This is a collection of three short novels that are linked together.
First, Rocannon's World, which includes part the short story "Semley's Necklace." Rocannon is a representative of the Hainish League, and he's gone to a world as yet unnamed by the Hain to talk to the people there and recruit them into the League, because the Enemy will attack them. His ship is destroyed, along with his teammates and all the records of their research, and he sets off to find the enemy's base on the world.
Second, Planet of Exile. Rolery is a native of Alterra, and Agat is a human born there, a descendant of League explorers. On Alterra, each season lasts fifteen years, and a person is lucky to remember two winters. At the end of every fall, the people from the north migrate south, usually in individual bands that pillage as they go. The people of Tevar, Rolery's people, build a winter city underground.
Except this time, the migrating people are all travelling together, and they've united their forces better to attack the wintering cities. Agat and the other humans warn them, but they go unheeded. When the raiders invade Tevar, the humans help evacuate the survivors and bring them to their city, where they jointly fight off the raiders.
Third, City of Illusions. A man who knows neither speech nor name appears in a clearing in the woods. The people who live there take him in, teach him speech and the Canons. After several years, he feels a need to go to Es Toch to learn about the Shing, and, if possible, regain his memory. He travels across the country, which millennia before was known as the United States, until he reaches Es Toch and learns who he really is.
These are all excellent stories, with LeGuin's typical skill at anthropological worldbuilding.