John Greenleaf Whittier (December 17, 1807 – September 7, 1892) was an American Quaker poet and forceful advocate of the abolition of slavery in the United States.

He was born to John and Abigail at the rural homestead in Haverhill, Massachusetts. He grew up on the farm in a household with his parents, a brother and two sisters, a maternal aunt and paternal uncle, and a constant flow of visitors and hired hands for the farm. During the winter term, he attended the district school, and was first introduced to poetry by a teacher.

Whittier was an activist all his life, although there is no record of him ever speaking in meeting, and, unlike some others who were Orthodox, he found time to engage in politics and championed abolitionism. Whittier became editor of a number of newspapers in Boston and Haverhill, as well as the New England Weekly Review in Hartford, Connecticut, the most influential Whig journal in New England. His first two published books were Legends of New England (1831) and the poem Moll Pitcher (1832). In 1838, a mob burned Whittier out of his offices in the antislavery center of Pennsylvania Hall in Philadelphia.

Highly regarded in his lifetime and for a period thereafter he is now remembered largely for the patriotic poem Barbara Frietchie, as well as for a number of poems turned into hymns, some of which remain exceedingly popular. Although clearly Victorian in style, and capable of being sentimental, his hymns exhibit both imagination and universalism of that set them beyond ordinary 19th century hymnody. Best known is probably Dear Lord and Father of Mankind taken from his poem The Brewing of Soma．

A bridge named for Whittier, built in the style of the Sagamore and Bourne Bridges spanning Cape Cod Canal, carries Interstate 95 from Amesbury to Newburyport over the Merrimack River. The city of Whittier, California, the community of Whittier, Alaska, the Minneapolis neighborhood of Whittier and the town of Greenleaf, Idaho were named in his honor. Both Whittier College and Whittier Law School are also named after him. In addition, an elementary school in Kenosha, Wisconsin is named Whittier School, as is one in Berkeley, California. Kenosha, built in 1927 as a two room school house, was expanded over the years and is currently one of the largest elementary schools in the Kenosha Unified School District.

Whittier's hometown of Haverhill, Massachusetts has named many buildings and landmarks in his honor including J.G. Whittier Middle School, Greenleaf Elementary, and Whittier Regional Vocational Technical High School. Whittier's family farm, John Greenleaf Whittier Homestead also called "Whittier's Birthplace" is now a historic site open to the public as is the John Greenleaf Whittier Home, his residence in Amesbury for 56 years.

The alternate history story P.'s Correspondence (1846) by Nathaniel Hawthorne, considered the first such story ever published in English, includes the notice "Whittier, a fiery Quaker youth, to whom the muse had perversely assigned a battle-trumpet, got himself lynched, in South Carolina". The date of that event in Hawthorne's invented timeline was 1835.

The small town of Greenleaf, Idaho is named in his honor.