Joseph P. Grinnell (February 27, 1877 – May 29, 1939) was an American field biologist and zoologist. He made extensive studies of the fauna of California, and is credited with introducing a method of recording precise field observations known as the Grinnell System. He served as the first director of the Museum of Vertebrate Zoology at the University of California, Berkeley from the museum's inception in 1908 until his death.

He edited The Condor, a publication of the Cooper Ornithological Club, from 1906 to 1939, and authored many articles for scientific journals and ornithological magazines. He wrote several books, among them The Distribution of the Birds of California and Animal Life in the Yosemite. He also developed and popularized the concept of the niche.

Joseph Grinnell was born February 27, 1877, the first of three children by his father Fordyce Grinnell MD and mother Sarah Elizabeth Pratt. Grinnell's father worked as the physician for the Kiowa, Comanche and Wichita Indian Agency near Fort Sill, Oklahoma. His distant cousins included the Massachusetts politician Joseph Grinnell (1788–1885) and George Bird Grinnell (1849–1938) who founded the Audubon Society. The Grinnells moved to the Pine Ridge Indian Agency in 1880.

In 1885 the Grinnell family moved to Pasadena, California, but the collapse of Southern California's boom forced Dr. Grinnell in 1888 to accept a position at the Indian school in Carlisle, Pennsylvania. The Carlisle Indian school commander was Captain Richard Henry Pratt, a friend of the Grinnells. Joseph Grinnell worked in a printing shop in Carlisle and collected his first specimen, a toad, before the family returned to Pasadena two years later.

Captain Pratt visited the Grinnells in Pasadena in 1896 while on a new assignment to inspect Indian Schools on the Pacific coast up to Alaska. The captain obtained permission from the family to take young Grinnell with him. Grinnell sent home bird specimens of the San Francisco Bay area, en route to Alaska. Captain Pratt completed his assignment and returned home. Grinnell remained in Alaska and continued collecting with the assistance of the Sheldon Jackson Museum in Haines, Alaska.

Grinnell went on field trips throughout the area, including remote Saint Lazaria Island. An unintended overnight stay on the island enabled him to study storm-petrels, an account of which he published in the March 1897 issue of the Nidologist, an early publication of the Cooper Ornithological Club.

Grinnell's expanding collection attracted visitors who were tourists, summer residents and visiting naturalists, including John Muir, Henry Fairfield Osborn, and ornithologist Joseph Mailliard. Grinnell returned to Pasadena in the fall of 1897 where he continued field work in the nearby mountains and canyons.

Grinnell's second visit to the far north began in 1898 on the schooner Penelope. He spent 18 months in Alaska during the Klondike Gold Rush. Grinnell corresponded regularly with his family, the letters were later compiled and edited into the book Gold Hunting in Alaska, published by David C. Cook Publishing Company in 1901. Grinnell joined the Long Beach and Alaska Mining and Trading Company to Kotzebue Sound, Alaska. The company landed at Cape Blossom in Kotzebue Sound in July 1898. Grinnell collected and observed the summer migrant bird life; Gambel's sparrow, barn swallow, and Savannah sparrow, among others. By August, Grinnell had 75 bird specimens preserved, including a Siberian yellow wagtail. The miners spent the winter inland on the Kowak River [Kobuk River], then returned to the coast that spring.