O Pioneers! is a 1913 novel by American author Willa Cather, written while she was living in New York. It is the first novel of her Great Plains trilogy, followed by The Song of the Lark (1915) and My Ántonia (1918).

Part I – The Wild Land

On a windy January day in Hanover, Nebraska, Alexandra Bergson is with her five-year-old brother Emil, whose little kitten has climbed a telegraph pole and is afraid to come down. Alexandra asks her neighbor and friend Carl Linstrum to retrieve the kitten. Later, Alexandra finds Emil in the general store with Marie Tovesky. They are playing with the kitten. Marie lives in Omaha and is visiting her uncle Joe Tovesky.

Alexandra's father is dying, and it is his wish that she run the farm after he is gone. Alexandra and her brothers Oscar and Lou later visit Ivar, known as Crazy Ivar because of his unorthodox views. For instance, he sleeps in a hammock, believes in killing no living thing and goes barefoot summer and winter. But he is known for healing sick animals. Alexandra is concerned about their hogs as the hogs of many of their neighbors are dying. Crazy Ivar advises her to keep their hogs clean rather than letting them live in filth and to give them fresh, clean water and good food. This simply confirms Oscar's and Lou's opinion that Ivar deserves the name Crazy Ivar. Alexandra, however, starts making plans for where she will relocate the hogs.After years of crop failure, many of the Bergson's neighbors are selling out, even if it means taking a loss. Then they learn the Linstrums have also decided to leave. Oscar and Lou want to leave too, but neither their mother nor Alexandra will. After visiting villages downwards to see how they are getting on, Alexandra talks her brothers into mortgaging the farm to buy more land, in hopes of ending up as rich landowners. 

Part II – Neighboring Fields

Sixteen years later, the farms are now prosperous. Alexandra and her brothers have divided up their inheritance, and Emil has just returned from college. The Linstrum farm has failed, and Marie, now married to Frank Shabata, has bought it. That same day, the Bergsons are surprised by a visit from Carl Linstrum, whom they have not seen for thirteen years.