Physicists contribute in various fields of sciences for a better understanding of our world. This is linked to the type of education they have to undergo. During their studies they are trained to solve problems, rather difficult and tricky problems in many cases. They like to do that, otherwise they would have chosen the wrong field for themselves. With this attitude in mind, they have made numerous significant contributions to such different fields as chemistry, biology, medicine, and what is of particular interest here, economics. Since physicists are used to working with equations, which represent their ideas in a transparent, logical, and consistent frame; they will naturally carry over that attitude to other fields in which they are working. This distinguishes them from those scientists who express their ideas solely in words and descriptions. The author of this volume, Reiner K¨ummel, is a physicist in the best sense. He received excellent training at world-renowned universities and despite considerable scientific success in a special field of physics, namely, superconductivity, he remained a generalist. What started as a hobby, namely, the study of the laws and driving forces of economics, rather soon became a serious occupation and a new branch of interdisciplinary work. His personal experiences, which he gained in different parts of the world, made him realize what former President Bill Clinton used as the 1992 campaign catch phrase: “It’s the economy, stupid!” After his studies in Germany Reiner K¨ummel spent his postdoctoral years in Urbana (Illinois) as an assistant of John Bardeen, one of the true giants of science. In the USA he experienced the prosperity and wealth of the world’s leading economic power. A few years later, he became acquainted with the life and struggle, of the people in Colombia, where he served for three years building up a master’s program at the Universidad del Valle in Cali in the spirit of Kennedy’s Peace Corps. The huge difference in living conditions between the USA and Germany, on the one hand, and Colombia, on the other, togetherwith his determination to do something to improve the lives of people, provided the background for his increasing engagement in economics. He realized rather soon that as a well-trained physicist he could make an important contribution to that field.