Four teenaged sisters and their mother, Marmee, live in a new neighborhood (loosely based on Concord) in Massachusetts in genteel poverty. Having lost all his money, their father is acting as a pastor, miles from home, involved in the American Civil War. The women face their first Christmas without him.
Meg and Jo March, the elder two, have to work in order to support the family: Meg teaches a nearby family of four children; Jo assists her aged great-aunt March, a wealthy widow living in a mansion, Plumfield. Beth, too timid for school, is content to stay at home and help with housework; Amy is still at school. Meg is beautiful and traditional, Jo is a tomboy who writes; Beth is a peacemaker and a pianist; Amy is an artist who longs for elegance and fine society.
Jo is impulsive and quick to anger. One of her challenges is trying to control her anger, a challenge that her mother experiences. She advises Jo to speak with forethought before leaving to travel to Washington, where her husband has pneumonia.
Their neighbour, Mr. Laurence, who is charmed by Beth, gives her a piano. Beth contracts scarlet fever after spending time with a poor family where three children die. Jo tends Beth in her illness. Beth recovers, but never fully. As a precaution, Amy is sent to live with Aunt March, replacing Jo, while Beth was ill and still infectious.
Jo has success earning money with her writing. Meg spends two weeks with friends, where there are parties for the girls to dance with boys and improve social skills. Theodore 'Laurie' Laurence, Mr. Laurence's grandson, is invited to one of the dances, as her friends incorrectly think Meg is in love with him. Meg is more interested in John Brooke, Laurie's young tutor. Brooke goes to Washington to help Mr. March. While with the March parents, Brooke confesses his love for Meg. They are pleased but consider Meg too young to be married. Brooke agrees to wait but enlists and serves a year or so in the war. After he is wounded, he returns to find work so he can buy a house ready for when he marries Meg. Laurie goes off to college. On Christmas Day, a year after the book's opening, the girls' father returns from the war.
(Published separately in the United Kingdom as Good Wives)
Three years later, Meg and John marry and learn how to live together. When they have twins, Meg is a devoted mother but John begins to feel left out. Laurie graduates from college, having put in effort to do well in his last year with Jo's prompting. He realises that he has fallen in love with Jo. Sensing his feelings, Jo confides in Marmee, telling her that she loves Laurie but she loves him like a brother and that she could not love him the romantic way. Laurie proposes marriage to her and she rejects him.
Jo decides she needs a break, and spends six months with a friend of her mother in New York City, serving as governess for her two children. The family runs a boarding house. She takes German lessons with Professor Bhaer, who lives in the house. He has come to America from Berlin to care for the orphaned sons of his sister. For extra money, Jo writes stories without a moral, which disappoints Bhaer. Amy goes on a European tour with her aunt. Laurie and his grandfather also go to Europe. Beth's health has seriously deteriorated. Jo devotes her time to the care of her dying sister. Laurie encounters Amy in Europe. With the news of Beth's death, they meet for consolation and their romance grows. Amy's aunt will not allow Amy to return with just Laurie and his grandfather, so they marry before returning home from Europe.
Professor Bhaer goes to the Marches' and stays for two weeks. On his last day, he proposes to Jo. Jo accepts. When Aunt March dies, she leaves Plumfield to Jo. She and Bhaer turn the house into a school for boys. They have two sons of their own, and Amy and Laurie have a daughter. At apple-picking time, Marmee celebrates her 60th birthday at Plumfield, with her husband, her three surviving daughters, their husbands, and her six grandchildren.