In the twenty-first century, the role and purpose of the so-called ‘museum store,’ the retail operation within non-profit museums, has become diverse and important as these outlets not only sell souvenirs, but also collaborate with artists and designers to produce unique objects and offer for sale exclusive products, contributing to the promotion and funding of the parent museums. Despite their increasing importance, however, museum stores have received little interest from academic and scholarly discourses including museum studies. This paper aims to argue the necessity of diverse explorations of museum stores as a division of museums, by offering case studies and discussing issues that may follow this research topic. I analyze the scarcity and limited purview of existing studies on the topic, and then discuss case studies. While there is currently no information on the origin of the first museum store, my study traces the early histories of the Metropolitan Museum of Art and the Museum of Modern Art in New York—two museums with the most prominent stores—and show that their early retail and publicity activities have been related to the museums’ missions to educate the public and that these histories are also linked to the identity of each museum store.