Daddy-Long-Legs is a romance about young Jerusha Abbot (who early on decides to go by Judy), an orphan at John Grier Home; an institute for orphans. Judy is sent off to college by one of the trustees of John Grier Home, who remains anonymous all through the story, until the end. The book is composed of Judy's letters to the trustee, whom she affectionately calls "Daddy-Long-Legs," due to his height, and rather long legs.

The story is of a young orphan's entrance into adulthood, freedom from the orphanage, and conflict between her loyalty to Daddy-Long-Legs and the gentleman she has fallen in love with. Through the personality Judy puts into her letters, and the sketches that are scattered amongst them (the portrait of Daddy-Long-Legs at left, and a picture of a spider at top; see credits), you really get a feel for what life would have been like for her, and actually know everything that goes on in the story, which is rare in books such as this.

While Maria is quite different from Daddy-Long-Legs, there are many similarities. For instance, Maria is sent to an expensive school by an unknown person who calls himself "Daddy Longlegs," and puts the condition on Maria to write letters to him often.