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, but also methods to support humans in the application of these theories 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 fields of applications on the other side is usually difficult to bridge. Some of us have experiences in such practical cooperation, 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 methods for successful applications in practice, but that we must develop a forum to present our results to a broader audience. First we must understand the s- nificant developments in our own group, which has activities in many directions of research.