Design practices and artifacts are ubiquitous. From a theoretical perspective the notion of design is taking on greater significance recently. Today, it goes far beyond the mere aesthetic embellishment of consumer products. In fact, design theories address that on a fundamental level realities are made. By that, they open an interdisciplinary field of research that exceed traditional notions of design as arts-and-crafts. This volume by head of IXDM Prof. Dr. Claudia Mareis is an introduction in pivotal design theories of the 20th century. It sketches out approaches and models that postulate an extended notion of design and establish interfaces to the humanities, science of technology as well as to society.