Joseph Jastrow (January 30, 1863– January 8, 1944) was an American psychologist, born in Warsaw, Poland. He was the son of Talmud scholar Marcus Jastrow. Joseph Jastrow came to Philadelphia in 1866, graduated at Penn in 1882, was a fellow in psychology at Johns Hopkins (1885-86), and was a professor at the University of Wisconsin from 1888 onwards.

Professor Jastrow was head of the psychological section of the World's Columbian Exposition in 1893. He contributed to the Psychological Review, and to other periodicals. His publications include:

• Time Relations of Mental Phenomena (1890)
• Epitomes of Three Sciences (1890)
• Fact and Fable in Psychology (1900)
• The Subconscious (1906)
• The Qualities of Men (1910)
• Character and Temperament (1914)
• The Psychology of Conviction (1918)
• Wish and Wisdom: Episodes in the Vagaries of Belief (1935)
• Story of Human Error (1936)

He also worked on the phenomena of optical illusions, and a number of well-known optical illusions (such as the Jastrow illusion