I. Magnin & Company was a San Francisco, California, based high fashion and specialty goods luxury department store. Over the course of its existence, it expanded across the West into Southern California and the adjoining states of Arizona, Oregon, and Washington. In the 1970s, under Federated Department Stores ownership, the chain entered the Chicago, and Washington, D.C., metropolitan areas. Mary Ann Magnin founded the company in 1876 and named the chain after her husband Isaac.

In the early 1870s, Dutch-born Mary Ann Magnin and her husband Isaac Magnin left England and settled in San Francisco. Mary Ann opened a shop in 1876 selling lotions and high-end clothing for infants. Later, she expanded into bridal wear. As her business grew, her exclusive clientele relied on her for the newest fashions from Paris. In the 20th century I. Magnin imported clothing by major designers including Jeanne Lanvin, Hattie Carnegie, and Christian Dior.

At the turn of the century, Mary Ann's four sons entered the business. While John, Grover, and Sam became associated with the I. Magnin store, the fourth son, Joseph, became known for his own store, Joseph Magnin Co.

The 1906 earthquake and fire leveled the San Francisco store with the remainder of the downtown area. The store reopened in new quarters at 50 Grant Avenue at Geary Boulevard in 1912. During the 1910s, the chain opened shops in six high-end hotels in California. The Los Angeles Wilshire Boulevard branch (opened in 1939) and the Union Square store (opened in 1948) were among the most elegant in the United States. When designer Christian Dior visited, he toured the Union Square store, and called it the "White Marble Palace".

Daughter Flora married Myer Siegel, who launched a namesake department store in Los Angeles, which would later become a chain. In Los Angeles in 1897 and 1898, I. Magnin & Co. advertised its wares for retail sale at 237 South Spring Street, noting that Mr. Myer Siegel was the manager. The I. Magnin store that Siegel managed moved to 251 S. Broadway on January 2, 1899; on June 19, 1904, I. Magnin announced that the Los Angeles store would henceforth be known as "Myer Siegel". I. Magnin would return with its own Los Angeles-area retail store later when it opened boutiques in the Maryland Hotel in Pasadena and the Ambassador Hotel in Mid-Wilshire, a branch at 6340 Hollywood Boulevard, and in 1939 a landmark store at 3240 Wilshire Boulevard near Bullocks Wilshire, designed by Myron Hunt, architect of the Ambassador Hotel.

In 1944, the chain was bought by the Los Angeles-based Bullock's department store chain. In the late 1950s the combined chain expanded into the Southern California suburbs by opening the Fashion Square concept in Santa Ana in 1958, the San Fernando Valley (Sherman Oaks) in 1962 and Del Amo (Torrance) in 1965.

After a major proxy battle in 1964, Bullocks-I. Magnin was merged into Federated Department Stores. Bullock's, I. Magnin, and eventually Bullocks Wilshire were run as separate divisions of Federated. I. Magnin expanded in the Chicago and Washington, D.C. areas in the 1970s.

R.H. Macy & Company had long yearned in the 1980s to enter the Southern California market. Along with trying to build their own stores, they attempted to purchase Federated, eventually losing a takeover war to the Campeau Corporation in 1988. As part of the settlement with Campeau, Macy's purchased Bullock's, Bullock's Wilshire and I. Magnin, subsequently beginning a reorganization of its divisions and consolidating the I. Magnin and Bullock's Wilshire stores into a semi-autonomous division under Macy's California. The seven Bullock's Wilshire stores were renamed I. Magnin in 1989.