S. Klein On The Square, or simply S. Klein, was a popular-priced department store chain based in New York City. The flagship stores (a main building and a women's fashion building) were located along Union Square East in Manhattan; this location would combine with the 1920s idiomatic catch phrase "on the square" (meaning "honest and straight-up") to provide the subtitle. S. Klein positioned itself as a step above regional discount stores of its time (Two Guys, Great Eastern Mills), more fashion aware than E. J. Korvette, and a more affordable option compared to traditional department stores like Macy's, or Abraham & Straus. S. Klein stores were full-line department stores, including furniture departments, fur salons, and full-service pet departments.

Russian-born Samuel Klein (1886–1942) founded S. Klein in 1905, or around 1912, on the block of Union Square East, between 14th and 15th Streets (in the former Union Square Hotel).