Four sisters, Meg, Jo, Beth and Amy March live in Concord, Massachusetts, with their mother. The sisters are initially distraught over the lack of presents at Christmas. Their father is away doing his part as a chaplain during the Civil War, and their mother, Marmee, doesn’t feel it is appropriate to spend money on gifts. The girls have a little hard-earned money saved up and decide to buy presents for themselves, but after their mother reads an inspiring letter from their father, the girls buy presents for their mother instead.
On Christmas, the girls receive books from Marmee and endeavor to read them every day so they may conquer their vices and embrace virtue. Marmee and her daughters cheerfully give their Christmas breakfast feast to a poor family named the Hummels. Their rich neighbor, Mr. Laurence, finds out about their charity and sends over treats.
The older girls, Meg and Jo, 16 and 15 respectively, are invited to a New Year's Eve party. Accident-prone Jo burns Meg's hair in an attempt to style it and wears slippers that are too snug. Meg is a natural beauty and full of grace. She dances until she sprains her ankle. Jo, with her dirty gloves and dress, which was scorched in back from her standing too close to the fire, sneaks away from the merriment. She feels more comfortable watching the festivities than partaking in them. To her delight, her neighbor Laurie, the grandson of Mr. Laurence, is also hiding. The two become fast friends.
Jo pursues her friendship with Laurie, leading to a friendship with his grandfather. Both boy and man fall in love with the sweet March family. Jo's younger sister Beth, 13, reminds Mr. Laurence of his deceased granddaughter. Shy and gentle Beth is a musical angel. Mr. Laurence wins her heart and gives the child a piano.
The girls work hard. Meg is a governess, and Jo a companion for their grumpy Aunt March. Beth maintains their home, and Amy goes to school to better herself. Amy is 12 and has golden curls, a love of drawing and a nose she finds far too flat. The young girl falls into trouble at school. She breaks a school rule by trading limes and is punished. Marmee does not approve of Amy's misbehavior or her teacher's method of dealing with it. Amy is pulled out of the school and educated at home.
Laurie and his tutor, Mr. Brooke, invite Meg and Jo to the theater. Amy is horribly disappointed she cannot attend. In her anger, she does the worst thing she can think of to Jo. Jo is a writer and has recently copied all of her works into one book, destroying all earlier editions. Amy throws the treasured book into the fire. Jo is so angry that she goes against the advice of Marmee and allows her anger for Amy to remain though Amy apologizes.
Jo and Laurie go ice-skating. Amy follows. Jo knows Amy is skating too close to thin ice, but she says nothing. Amy falls through. Laurie comes to the rescue, and Laurie and Jo get Amy home safely. Jo is horrified at herself for allowing her sister to be harmed. She forgives Amy and commits to better controlling her temper.
The sisters start a lovely club called the Pickwick Club. They make their own newspaper, write and act out plays, and even admit Laurie as a member.
Marmee allows the sisters to learn a valuable lesson. The girls want to try a week of all fun and no work. Though each girl is free to indulge her passions and whims — Jo reading, Amy drawing, Meg improving her clothes and Beth playing piano — they find themselves inexplicably irritable. Beth is horrified when she finds her pet bird dead from neglect. To drive the lesson home, Marmee abandons them on the last day, and Jo tries to throw a dinner party without her or their housekeeper, Hannah. The food is a disaster, but wise Marmee teaches the girls that a healthy life consists of a proper balance of work and play.
Laurie plans his own party — a picnic with friends from England and the March family. All have a lovely time, with even shy Beth making friends with a boy who has an injured leg. Though a rich young man shows interest in Meg, she finds herself enjoying Mr. Brooke and his fine brown eyes.
A telegram wreaks havoc in the life of the March family. Mr. March is very ill. Money has to be borrowed from Aunt March, and Jo sells her hair so Marmee may have more funds to take with her to Washington, D.C. Marmee leaves to attend to their father. Mr. Brooke accompanies her.
Initially the girls attend to their duties faithfully. But while Marmee is away, things change. Beth ends up caring for the Hummels, largely on her own, and contracts scarlet fever. Amy has to be sent away to live with Aunt March for her safety. Beth grows sicker, but Hannah does not want to bother Mrs. March. Eventually Laurie intervenes, and Mrs. March comes home. Beth recovers under her mother's care.
Amy matures under the well-meaning but strict care of her aunt and relies on Laurie to keep her spirits up. Laurie guesses that Meg and Mr. Brooke are falling in love. He pulls a prank that accelerates Meg's feelings for Mr. Brooke. Jo is both angry and sad that her sister is growing up and afraid of the time when she will marry and move on.
Christmas comes again, and Mr. March surprises the family by coming home. Mr. Brooke and Meg are engaged.
Three years pass. Then Meg marries Mr. Brooke. They are very poor but very happy in their mutual love and respect for one another. They have twins, and Meg neglects her husband for a time to care for them. But good advice from Marmee sets her world right again. Meg learns to allow her husband to help her with the children, and they have a family rich in love that even Meg's rich friends envy.
Amy goes abroad with Aunt March. If not for Jo's rude tongue, she may have gotten to go. Amy improves greatly overseas as an artist and as a lady in society.
Jo continues to write. She wins a contest and is paid to write a column. Laurie is in college, but comes home frequently, trying in vain to win Jo's heart. Jo fears that he is in love with her and hopes that Laurie may love Beth in time instead. Jo goes off to New York City to get out of the way of what she hopes will be a romance.
In New York City, Jo is a governess for girls whose mother runs a boarding house. Jo meets a young German professor. Though poor, he always has treats for children and kindness for all. He protects Jo from the negative influences in New York City by tactfully convincing her to give up writing sensational novels devoid of morals. Jo misses the money, but knows her parents would not approve of her doing that kind of writing. He also intervenes when Jo overhears an intellectual conversation that makes her question her faith.
Jo returns home to heartache. She breaks Laurie's heart by refusing to marry him. Laurie and his grandfather go overseas, giving him time and space to heal. Beth’s health is deteriorating. Beth and Jo go away together on a trip, and Jo discovers Beth is dying. When they return, the family spends the year making Beth as comfortable as possible. Amy is not sent for and is still overseas when Beth dies.
Laurie and Amy grow quite close. They eventually fall in love and are married. Jo is delighted that her friend is finally her brother. Jo's German professor visits her town. Jo finds the death of Beth has changed her, and she is now open to love. The two end up engaged, and after years of waiting, wed.
They open a school for boys at Plumfield, which is Aunt March's estate. When Aunt March died, she left it to Jo. Jo and her husband have two boys. Amy and Laurie have a daughter whom they name Beth. Their daughter is sickly, and they fear she may not stay long in this world.
The novel ends with the whole family together — the old generation and the new.