The term inrō derives from the Sino-Japanese roots in (from Middle Chinese 'jin 印 "printed") and rō (MC luwng 籠 "cage"). Because traditional Japanese robes lacked pockets, objects were often carried by hanging them from the obi, or sash, in containers known as sagemono (a Japanese generic term for a hanging object attached to a sash). Most sagemono were created for specialized contents, such as tobacco, pipes, writing brush and ink, but the type known as inrō was suitable for carrying anything small.
Consisting of a stack of tiny, nested boxes, inrō were most commonly used to carry identity seals and medicine. The stack of boxes is held together by a cord that is laced through cord runners down one side, under the bottom, and up the opposite side. The ends of the cord are secured to a netsuke, a kind of toggle that is passed between the sash and pants and then hooked over the top of the sash to suspend the inrō. An ojime, or bead, is provided on the cords between the inrō and netsuke to hold the boxes together. This bead is slid down the two suspension cords to the top of the inrō to hold the stack together while the inrō is worn, and slid up to the netsuke when the boxes need to be unstacked to access their contents. Inrō were made of a variety of materials, including wood, ivory, bone, and lacquer. Lacquer was also used to decorate inro made of other materials.
Inrō, like the ojime and netsuke they were associated with, evolved over time from strictly utilitarian articles into objects of high art and immense craftsmanship.