New Jersey is a state situated within both the Mid-Atlantic and Northeastern regions of the United States. It is the most densely populated U.S. state, and is situated at the center of the Northeast megalopolis, the most populous urban agglomeration in the nation. New Jersey is bordered on its north and east by New York state; on its east, southeast, and south by the Atlantic Ocean; on its west by the Delaware River and Pennsylvania; and on its southwest by Delaware Bay and Delaware. At 7,354 square miles (19,050 km²), New Jersey is the fifth-smallest state in land area, but with close to 9.3 million residents as of the 2020 United States census, its highest decennial count ever, ranks 11th in population. The state capital is Trenton, and the state's most populous city is Newark. New Jersey is the only U.S. state in which every county is deemed urban by the U.S. Census Bureau with 13 counties included in the New York metropolitan area, seven counties in the Philadelphia metropolitan area, and Warren County constituting part of the rapidly industrializing Lehigh Valley metropolitan area.

New Jersey was first inhabited by Paleo-Indians as early as 13,000 B.C.E., with the Lenape being the dominant indigenous group when Europeans arrived in the early 17th century. Dutch and Swedish colonists founded the first European settlements in the state, with the British later seizing control of the region and establishing the Province of New Jersey, named after the largest of the Channel Islands. The colony's fertile lands and relative religious tolerance drew a large and diverse population. New Jersey was among the Thirteen Colonies that supported the American Revolution, hosting numerous pivotal battles and military commands in the American Revolutionary War. On December 18, 1787, New Jersey became the third state to ratify the United States Constitution, and thus be admitted to the Union, and was the first state to ratify the U.S. Bill of Rights on November 20, 1789.

New Jersey remained in the Union during the American Civil War and provided troops, resources, and military leaders in support of the Union Army. After the war, the state emerged as a major manufacturing center and a leading destination for immigrants, helping drive the Industrial Revolution in the U.S. New Jersey was the site of many industrial, technological, and commercial innovations, including the first town (Roselle) to be illuminated by electricity, the first incandescent light bulb, and the first steam locomotive. Many prominent Americans associated with New Jersey have proven influential nationally and globally, including in academia, advocacy, business, entertainment, government, military, non-profit leadership, and other fields.

New Jersey's central location in the Northeast megalopolis helped fuel its rapid growth and suburbanization in the second half of the 20th century. At the turn of the 21st century, its economy increasingly diversified, with major sectors including biotechnology, pharmaceuticals, specialized agriculture, and information technology. New Jersey remains a major destination for immigrants and is home to one of the most ethnically diverse and multicultural populations in the world. Echoing historical trends, the state has increasingly re-urbanized, with growth in cities outpacing suburbs since 2008. New Jersey is one of the wealthiest states in the U.S., consistently ranking as one of the top three by median household income. Almost one-tenth of all households, or over 323,000 of 3.3 million, are millionaires, the highest rate of any U.S. state. New Jersey's public school system consistently ranks at or among the top of all U.S. states. According to climatology research by the U.S. National Oceanic and Atmospheric Administration, New Jersey has been the fastest-warming state by average air temperature over a 100-year period beginning in the early 20th century, due to persistent warming of the North Atlantic Ocean.