The story opens in Concord, Massachusetts, just a few days before Christmas in the year 1860. The four March girls – motherly Meg (age 16), boyish Jo (age 15), frail yet pious Beth (age 13), and elegant Amy (age 12) – live alone with their mother, Mrs. March. Their father, Mr. March, has volunteered to serve in the Union army as a chaplain, leaving his wife and daughters to fend for themselves in his absence. Though impoverished, the March family is rich in spirit; they are bolstered by their familial love and steered by strong Christian morals. On Christmas morning, the girls wake to discover that they’ve each received a copy of Pilgrim’s Progress, an allegorical novel about Christian morals. Together, they resolve to read a little from their books each day, and to put the morals they learn into practice. While attending a dance thrown by a local rich family, Meg and Jo meet Laurie, the grandson of the March family’s rich neighbor, Mr. Laurence. Laurie becomes a fixture at the March household, and old Mr. Laurence befriends the girls and becomes a surrogate grandfather to them. Laurie’s tutor, Mr. Brooke, also becomes a fixture in the March household, and he takes a special liking to Meg.
Over the course of the following year, the girls encounter a number of trials that put their readings of Pilgrim’s Progress to the test. Vain Meg, for instance, burns off a lock of her hair, conceited Amy is beaten in front of her classmates at school when she’s discovered hoarding pickled limes in her desk, and Jo (blinded by anger) carelessly allows Amy to fall into an icy river. Toward the end of the year, they learn their father has fallen ill, and Mrs. March travels to Washington, D.C. (accompanied by Mr. Brooke) in order to tend to him. While Mrs. March is away, Beth contracts scarlet fever, and she grows so sick that the March girls and their servant Hannah fear that she won’t survive. Beth’s sickness finally abates the morning Mrs. March returns from Washington, much to everyone’s relief. On Christmas, Laurie surprises Mrs. March and her daughters with the news that Mr. March has come home early. Mr. March surveys his daughters and is pleased with their moral growth in his absence. Soon after, Mr. Brooke confronts Meg and asks for her hand in marriage. She accepts, with the stipulation that they should wait three years before marrying, and the March family (with the exception of Jo, who wishes for her sister to remain at home) is awash in celebration.
Part II opens with Meg’s wedding to Mr. Brooke. The ceremony is a simple affair held at the March family’s home. She and Mr. Brooke then begin their new life at their modest home, the Dovecote. Meg gives birth to twins, Daisy and Demi, not long afterward. Jo, meanwhile, is pursuing her writing in earnest; she soon sells several of her stories and poems to a local newspaper; she uses the proceeds from her publications to send Beth and Mrs. March on holiday. Amy, given her elegant manners, has become rich Aunt March’s confidante. Amy also impresses a distant yet wealthy relative, Aunt Carrol, who decides to take Amy with her on a trip to Europe. Soon after, Jo decides to move to New York for the winter in order to evade Laurie, who is infatuated with Jo. While working as a governess in a boarding house, Jo meets a kindhearted German professor named Friedrich Bhaer.
When Jo returns home after her stint in New York, Laurie confronts her and asks for her hand in marriage. Jo turns him down, and Laurie is devastated. Mr. Laurence then takes him on a trip to Europe, where Laurie soon runs into Amy. Meanwhile, back at home, Beth’s health is waning. Jo takes her on one last holiday to the seashore, and Beth dies not long after. Word of Beth’s death reaches Amy, who finds solace in her friendship with Laurie. Laurie realizes Amy was his true love all along; the two fall in love and elope. They return home the night before Jo’s 25th birthday. That same night, Professor Bhaer makes a surprise visit. He proposes to Jo toward the end of his visit, and Jo accepts.
Five years pass. Jo and Bhaer are married, they have two boys, and they inherit Aunt March’s house when she dies. Jo and Bhaer turn it into a school called Plumfield. The book ends with the celebration of Mrs. March’s 60th birthday. The entire March family gathers in the apple orchard and reflects on how blessed they are to have each other. Mrs. March reflects that there is no greater happiness than to experience the love she has for her family.