Little Dorrit is a novel by English author Charles Dickens, originally published in serial form between 1855 and 1857. The story features Amy Dorrit, youngest child of her family, born and raised in the Marshalsea prison for debtors in London. Arthur Clennam encounters her after returning home from a 20-year absence, ready to begin his life anew.

The novel satirises some shortcomings of British society and government at the time, including the institution of debtors' prisons, where debtors were imprisoned, unable to work and yet incarcerated until they had repaid their debts. The prison in this case is the Marshalsea, where Dickens's own father had been imprisoned. Dickens is also critical of the inert bureaucracy of the British government, in this novel in the form of the fictional "Circumlocution Office". In addition, Dickens satirises the stratification of society that results from the British class system.

In 1826 Marseille, murderer Rigaud narrates to his prison cellmate John Baptist Cavalletto how he had killed his wife, just prior to being taken to trial. Businessman Arthur Clennam is detained with other travelers in quarantine in Marseilles and becomes friends with the merchants Mr. and Mrs. Meagles, their daughter "Pet", and their maid, an orphan named Harriet Beadle whom the family has nicknamed Tattycoram. Arthur has spent the last twenty years in China with his father, handling that part of the family business; his father died recently there. Arthur is now returning to London to see his mother, Mrs Clennam.

When Arthur's father was on his deathbed, he gave Arthur a watch to give to his mother with a message inside, murmuring "Your mother," which Arthur delivers to Mrs. Clennam. Inside the watch casing is an old silk paper with the initials DNF (do not forget) worked in beads. Arthur asks about the message, but Mrs. Clennam, who now uses a wheelchair, refuses to reveal what it means. Arthur says that he will not continue in the family business and will seek new opportunity on his own. Jeremiah Flintwinch then presses Mrs. Clennam on her failure to tell Arthur of the past.

In London, William Dorrit, imprisoned as a debtor, has been a resident of Marshalsea debtors' prison for over twenty years. He has three children: Edward (known as Tip), Fanny and Amy. The youngest daughter, Amy, was born in the prison and is affectionately known as Little Dorrit. Their mother died when Amy was eight years old. Tip has recently been imprisoned for his own gambling debts, and Fanny lives outside the prison with William's older brother Frederick. She works as a dancing girl in the music hall (where Frederick plays the clarinet) and has attracted the attention of the wealthy Edmund Sparkler. Little Dorrit, devoted to her father, supports them both through her sewing and is free to pass in and out of the prison. To maintain the honour of her father, who is embarrassed to acknowledge his financial position, Little Dorrit avoids mentioning her work outside the prison or his inability to leave. Mr Dorrit assumes the role of Father of the Marshalsea and is held in respect by its inhabitants, as if he had chosen to live there.

After Arthur tells his mother that he will not continue in the family business, Mrs. Clennam chooses her clerk Jeremiah Flintwinch as her partner. When Arthur learns that Mrs. Clennam employs Little Dorrit as a seamstress and shows her unusual kindness, he wonders whether the young girl might be connected with the watch's mystery. Arthur follows the girl to the Marshalsea. He tries in vain to enquire about William Dorrit's debt in the Circumlocution Office – assuming the role of benefactor towards Little Dorrit, her father, and her brother. Meanwhile, Rigaud, who has been released for lack of evidence, approaches Mrs. Clennam under the name Blandois and blackmails her and Flintwinch into giving him a place in her business.

While at the Circumlocution Office, Arthur meets successful inventor Daniel Doyce. Doyce wants a partner and man of business at his factory, and Arthur agrees to fill that role. Arthur encounters Cavalletto, who is injured by a carriage in London, and aids him in getting medical care. Cavalletto lives in hopes of never again seeing Blandois. Little Dorrit falls in love with Arthur, who fails to recognise her feelings. He is infatuated with Pet Meagles but is disappointed when she marries the cruel artist Henry Gowan. After Pet's wedding, the Meagles family suffers a blow when Tattycoram runs away to live with traveler Miss Wade.

Arthur becomes reacquainted with his former fiancée Flora Finching, the reason he was sent away to China. She is now a widow and takes care of the aunt of her late husband. Her father Mr Casby owns many rental properties, and his rent collector, Mr Pancks, takes the brunt of the dirty work of collecting Casby's inflated rents. Pancks discovers that William Dorrit is the lost heir to a fortune, enabling him to pay his way out of prison and altering the status of the entire family. Restored to wealth, Dorrit shuns all reminders of his past and forbids a heartbroken Little Dorrit from seeing Arthur again.