Randalls Island (sometimes called Randall's Island) and Wards Island are conjoined islands, collectively called Randalls and Wards Island, in New York City. Part of the borough of Manhattan, it is separated from Manhattan Island by the Harlem River, from Queens by the East River and Hell Gate, and from the Bronx by the Bronx Kill. A channel named Little Hell Gate separated Randalls Island to the north from Wards Island to the south; the channel was filled by the early 1960s. A third, smaller island, Sunken Meadow Island, was located east of Randalls Island and was connected to it in 1955.

The Lenape Native Americans, who lived in the New York City area before European colonization, did not inhabit the islands. Between the 1630s and the 1770s, the islands had various European residents; the islands had the same owners in the 17th century, but ownership was split during the 18th century. Randalls and Wards Islands became known for their respective early-19th-century owners, Jonathan Randel and the Ward brothers. The city government took over both islands in the mid-19th century and developed numerous hospitals, asylums, and cemeteries there. Most of the existing buildings were demolished starting in the 1930s, when the Triborough (now Robert F. Kennedy) Bridge, two parks, and a wastewater treatment plant were developed there. The islands have since been connected with each other, and various recreational facilities and institutions have been developed on both islands in the late 20th and the 21st centuries.

Most of Randalls and Wards Island is parkland with athletic fields, a driving range, greenways, playgrounds, picnic grounds, and the Icahn Stadium track-and-field facility. The island is home to several public facilities, including a psychiatric hospital, an addiction treatment facility, shelters, a fire training academy, police station, and a wastewater treatment plant. The modern-day island is crossed by the Robert F. Kennedy and Hell Gate bridges.

What is now Randalls and Wards Island was originally composed of Randalls Island to the north, Wards Island to the south, and Sunken Meadow just southeast of Randalls Island. A small creek, Little Hell Gate, ran between the islands. The current Randalls and Wards Island came about when Little Hell Gate was partially infilled. The combined island is part of the New York City borough of Manhattan; this dates to an 1829 statute that designated the islands as being within Manhattan's eastern boundary. Randalls and Wards Island has an area of about 530 acres (210 ha). The island is surrounded by Bronx Kill to the north, separating it from the Bronx; Harlem River to the west, separating it from Manhattan Island; and the Hell Gate channel of the East River to the south and east, separating it from Queens. The island had a population of 1,648 in 2010.

A small island called Mill Rock exists south of Wards Island, while further south is Roosevelt Island. Prior to the removal of Hell Gate rocks in the mid-19th century, there were other large rock outcroppings in the East River near Wards Island.

Before the islands were combined, Randalls Island had an area of about 240 acres (97 ha). Randalls Island had some granite outcroppings and marshland. The southern part of the island was composed of low hills, while the northern two-thirds were higher and flatter. There were two isolated ponds on the northern part of the island. There was a ridge across the island's northern section, which hosted farms and fruit orchards in the 19th century. Surrounding Randalls Island was a narrow strip of marshland, and there were larger marshes to the north and southeast, which drained into the East River. The north and southeast shores also had shellfish beds. The southern part of the island was leveled, and the shoreline rebuilt, in the mid-19th century, though some meadows and swamps remained until the 1930s.

To the east of Randalls Island was Sunken Meadow Island, which covered about 20 acres (8.1 ha). Ownership of Sunken Meadow Island had been disputed during the early 20th century, and city officials had considered that island to be part of Randalls Island. Infilling took place beginning in the mid-1950s. The Sunken Meadow section of Randalls Island Park comprises 85 acres (34 ha) and contains ball fields. Also east of Randalls Island was an even smaller island called the Hammock, which was subsumed through filling operations.

Originally, Wards Island had an area of about 145 acres (59 ha). Like Randalls Island to the north, Wards Island had marshlands on its western and northern shores and shellfish beds on the southeastern part of the island. A 1968 guidebook described grasses as being present across the island. The island is surrounded by piles of riprap or rocks.