Michael Bernard Bloomfield (July 28, 1943 – February 15, 1981) was an American blues guitarist and composer. Born in Chicago, he became one of the first popular music stars of the 1960s to earn his reputation almost entirely on his instrumental prowess, as he rarely sang before 1969. Respected for his guitar playing, Bloomfield knew and played with many of Chicago's blues musicians before achieving his own fame and was instrumental in popularizing blues music in the mid-1960s. In 1965, he played on Bob Dylan's Highway 61 Revisited, including the single "Like a Rolling Stone", and performed with Dylan at that year's Newport Folk Festival.

Bloomfield was ranked No. 22 on Rolling Stone's list of "100 Greatest Guitarists of All Time" in 2003 and No. 42 by the same magazine in 2011. He was inducted into the Blues Hall of Fame in 2012 and, as a member of the Paul Butterfield Blues Band, was inducted into the Rock and Roll Hall of Fame in 2015.

Bloomfield was born in Chicago into a wealthy Jewish family. Bloomfield's father, Harold, was born there in 1914. Harold's father, Samuel Bloomfield, started Bloomfield Industries in the early 1930s. After Samuel's death, Harold and his brother, Daniel, inherited the company. Bloomfield's mother, Dorothy Klein, was born in Chicago in 1918 and married Harold in 1940. She came from an artistic, musical family, and worked as an actress and model before marrying.

Bloomfield's family lived in various locations around Chicago before settling at 424 West Melrose Street on the North Side. When he was twelve his family moved to suburban Glencoe, where he attended New Trier High School for two years. During this time, he began playing in local bands, then put together one called the Hurricanes, named after Ohio rock band Johnny and the Hurricanes. New Trier expelled Bloomfield after his band performed a raucous rock and roll song at a 1959 school gathering. He attended Cornwall Academy in Massachusetts for one year and then returned to Chicago, where he spent his last year of education at a local Central YMCA High School.

Bloomfield had attended a 1957 Chicago performance by blues singer Josh White, and began spending time in Chicago's South Side blues clubs and playing guitar with such black bluesmen as Sleepy John Estes, Yank Rachell, and Little Brother Montgomery. He first sat in with a black blues band in 1959, when he performed with Luther "Guitar Junior" Johnson at a Chicago club called the Place. He performed with Howlin' Wolf, Muddy Waters, and many other Chicago blues performers during the early 1960s. In 1962 he married Susan Smith.

Writing in 2001, keyboardist, songwriter and record producer Al Kooper said:

[Bloomfield] had a certain innate talent for playing the guitar that was instantly obvious to his mentors. They knew this was not just another white boy; this was someone who truly understood what the blues were all about. Among his early supporters were B.B. King, Muddy Waters, Bob Dylan and Buddy Guy. Michael used to say, "It's a natural. Black people suffer externally in this country. Jewish people suffer internally. The suffering's the mutual fulcrum for the blues."

In the early 1960s he met harmonica player and singer Paul Butterfield and guitarist Elvin Bishop, with whom he would later play in the Paul Butterfield Blues Band. He also began friendships and professional associations with fellow Chicagoan Nick Gravenites and Bronx-born record producer Norman Dayron, who was attending the University of Chicago. He developed a friendship with blues singer Big Joe Williams. In 1963 Bloomfield and his two friends George Mitchell and Pete Welding ran a weekly blues showcase at the Fickle Pickle. He subsequently built up his reputation in two Chicago clubs, Big John's and Magoo's. With help from his friend Joel Harlib, a Chicago photographer who became Bloomfield's de facto manager, he became a Columbia Records recording artist. In early 1964 Harlib took an audition tape by Bloomfield to Columbia producer and talent scout John Hammond, who signed him to Columbia's Epic Records label.