Andrew Rosen is a pioneer in the contemporary fashion market, co-founding Theory with Elie Tahari in 1997. In 2019, he stepped down as chief executive of the company, but will remain in an advisory role, spending half of his time on Theory and the other half on other pursuits. Rosen also backs several labels including Rag & Bone and Alice + Olivia
Rosen sold the majority of his Theory shares in 2003 to Japan's Fast Retailing, but retains an 11 percent share and continued to run the company until 2019. He has a particularly strong relationship with Theory’s owner, Tadashi Yanai , whose company Fast Retailing also owns Uniqlo and J Brand.
Following the sale of Theory, Rosen invested $10 million dollars in emerging designers. Rosen's portfolio of investments includes Alice + Olivia and Rag & Bone. He sold his stake in Proenza Schouler in 2014, to LVMH. Rosen also has stakes in Kiki de Montparnasse, Aiko and Gryphon. By 2012, they had evolved into businesses with combined sales of over $300 million, prompting Vogue editor-in-chief Anna Wintour to say, “We don’t have a Gucci or LVMH in this country, but in his own way, Andrew is creating a kind of American equivalent.”
Rosen was arguably the first to identify the gap in the United States and international markets for fashionable contemporary brands. In response to the shifting consumer market, Rosen hired designer Olivier Theyskens , whose aesthetic was well-received in the Asian market, to head up Theory’s design team as creative director, as well as acting as creative director of the newly created Theyskens’ Theory, an advanced contemporary line. Most recently, he hired Francesco Fucci, a former design director at The Row, whose particular flavour of minimalism has brought a refinement to the collections. Rosen has also experimented with sub-brands, creating Theory 2.0, a capsule designed and built by an in-house team of rising stars from across the company, in 2017.