Lake Winnipesaukee is the largest lake in New Hampshire. It is approximately 21 miles (34 km) long (northwest-southeast) and from one to nine miles (1.6 to 15 km) wide (northeast-southwest), covering 69 square miles (180 km²) (71 square miles when Paugus Bay is included), with a maximum depth of 212 feet (64.6 meters).

The lake contains at least 253 islands, half of which are less than a quarter-acre in size (list of islands) and is indented by several peninsulas, yielding a total shoreline of some 288 miles. The driving distance around the lake is 63 miles. It is 504 feet (153 m) above sea level. Winnipesaukee is the third-largest lake in New England after Lake Champlain and Moosehead Lake.

Lake Winnipesaukee has been a tourist destination for more than a century, especially for residents escaping the summer heat of Boston and New York City. The Native American name Winnipesaukee means either "smile of the Great Spirit" or "beautiful water in a high place". At the outlet of the Winnipesaukee River, the Winnipesaukee Indians, a subtribe of the Pennacook, lived and fished at a village called Acquadocton. The site is today called The Weirs, named for the weirs colonists discovered when first exploring the region.

Winnipesaukee is a glacial lake and an unusual one at that, since the last glaciation actually reversed the flow of its waters. Draining the central portion of New Hampshire, it once flowed southeast, leaving via what is now Alton Bay toward the Atlantic Ocean. When glacial debris blocked this path, flow was redirected westward through Paugus Bay into the Winnipesaukee River. The latter flows west from the lake and joins the Pemigewasset River in Franklin to form the Merrimack River, which flows south to Massachusetts and into the Atlantic.

Center Harbor witnessed the first intercollegiate sporting event in the United States, as Harvard defeated Yale by two lengths in the first Harvard-Yale Regatta on August 3, 1852. The outcome was repeated 100 years later when the schools celebrated the centennial of the race by again competing on Lake Winnipesaukee.

More recently, Lake Winnepesaukee has become a significant tourist attraction in New Hampshire; French President Nicolas Sarkozy took his first vacation in office in August 2007 at Wolfeboro on the lake.

Lake Winnipesaukee was also where the eponymous Lake Winnipesaukee mystery stone was found.