Corie is a young, vivacious, and highly optimistic newlywed. She possesses a sunny, adventurous nature and prefers to view her fifth-floor walk-up apartment's flaws, such as a hole in the skylight and no bathtub, as charming quirks. Driven by emotion and impulsivity, she throws herself into experiences without much forethought and expects those around her to match her level of enthusiasm.

Paul is a 26-year-old lawyer who dresses and acts much older than his age. He is highly pragmatic, straight-laced, and intensely focused on his budding legal career. He values logic and control, making him highly critical of the unheated, poorly maintained apartment and anxious about any deviations from his daily routine.

Ethel is Corie's widowed mother, an attractive woman in her late 40s who focuses her energy almost entirely on her daughter rather than her own life. She is reserved, cautious, and prone to physical complaints like back pain and a sensitive stomach. Though she claims to be content with her quiet routine in New Jersey, she reluctantly goes along with the adventurous demands of those around her to keep the peace.

Victor is a 58-year-old eccentric neighbor living in the Bratters' building. Known locally as the Bluebeard of 48th Street, he is highly adventurous and claims to enjoy skiing and mountain climbing, though he is currently four months behind on rent. He is highly creative, famously preparing an exacting eel dish called knichi for guests, but lacks practicality in his day-to-day affairs.

Harry is a heavy-set telephone repairman in his mid-thirties who installs the communication lines in Corie and Paul's new apartment. Wearing a plaid wool jacket and baseball cap, he brings a practical, working-class perspective to the apartment's physical limitations.

Harriet is Corie's aunt who lives in New Jersey. She keeps tabs on Ethel's daily routine and alerts the family when there is cause for alarm regarding her schedule.