This gracious classic nine-room residence offers a rare opportunity to create an expansive home at the distinguished 850 Park Avenue. Situated on the fifth floor, the apartment enjoys eastern exposures over Park Avenue along with southern and western light, creating a home that is both bright and quiet. Entry is via a semi-private landing that opens into a generous formal gallery, elegantly separating the public entertaining spaces from the private quarters. The large living room and formal dining room are ideal for entertaining, while the adjacent library offers flexibility as a den, office, or additional bedroom. Just beyond the dining room is the service wing, which includes a butler's pantry, a generously proportioned windowed kitchen, a full bathroom, and a separate staff room. The three well-proportioned bedrooms are privately positioned along the southern side of the apartment. The corner primary bedroom features an en-suite bathroom, while the second and third bedrooms share a well-appointed bathroom between them. Additional features include 10-foot ceilings, a wood-burning fireplace, original herringbone oak floors, and large windows throughout, The offering also includes a large private office or staff room with a full bathroom conveniently located across the hall on the same floor, ideal for use as a home office, guest suite, or additional staff accommodation. Designed in 1914 by the architectural firm Rouse & Goldstone, 850 Park Avenue is a prestigious Upper East Side white-glove cooperative offering the highest level of service, including 24-hour door staff and a live-in superintendent. Building amenities include a fitness room, bike room, children's play area, basketball half-court, landscaped courtyard, and private storage. Pets are permitted. Pied-à-terre ownership is considered on a case-by-case basis. Financing of up to 30% is allowed, and a 2.5% flip tax is payable by the purchaser.