Jerusha Abbott was brought up at the John Grier Home, an old-fashioned orphanage. The children were wholly dependent on charity and had to wear other people's cast-off clothes. Jerusha's unusual first name was selected by the matron off a grave stone, while her surname was selected out of the phone book. At the age of 18, she has finished her education and is at loose ends, still working in the dormitories at the institution where she was brought up.

One day, after the asylum's trustees have made their monthly visit, Jerusha is informed by the asylum's dour matron that one of the trustees has offered to pay her way through college. He has spoken to her former teachers and thinks she has potential to become an excellent writer. He will pay her tuition and also give her a generous monthly allowance. Jerusha must write him a monthly letter, because he believes that letter-writing is important to the development of a writer. However, she will never know his identity; she must address the letters to Mr. John Smith, and he will never reply.

Jerusha catches a glimpse of the shadow of her benefactor from the back, and knows he is a tall long-legged man. Because of this, she jokingly calls him "Daddy Long-Legs." She attends a women's college, but the name and location are never identified; however, men from Princeton University are frequently mentioned as dates, so it is certainly on the East Coast. The college is almost certainly based on the author's alma mater, Vassar College, judging from college traditions mentioned. She illustrates her letters with childlike line drawings, also created by Jean Webster. (Summary by Wikipedia)