This volume contains selected papers presented at the 12th International C- ference on Conceptual Structures, ICCS 2004, held in Huntsville Alabama, July 19-23, 2004. The main theme of the conference, "Conceptual Structures at Work", was chosen to express our intention of applying conceptual structures for hum- centered practical purposes. That invites us to develop not only clear conceptual theories,butalsomethodstosupporthumansintheapplicationofthesetheories in their societies. Some promising steps in this direction are being taken, but the gap between the researchers working on a highly sophisticated level on one side and the practitioners in many ?elds of applications on the other side is usually di?culttobridge.Someofushaveexperiencesinsuchpracticalcooperation,but we need more members of our community to be engaged in "real life problems". We all know that solutions of complex problems in practice require not only a well-developed formal theory, but also an understanding of the whole context of the given problems. To support our understanding we need general philo- phical methods as well as formal theories for the representation of fundamental structures in practice. We believe that our community has powerful tools and methodsforsuccessfulapplicationsinpractice,butthatwemustdevelopaforum to present our results to a broader audience. First we must understand the s- ni?cant developments in our own group, which has activities in many directions of research.