This compact introduction to the ordinary differential equations and their applications is aimed at anyone who, in their studies, is confronted voluntarily or involuntarily with this versatile subject. Numerous examples from physics, technology, biomathematics, cosmology, economy and optimization allow a quick and motivating approach - abstract proofs and unnecessary formalism are avoided as far as possible. In the foreground is the modelling of ordinary differential equations of the 1st and 2nd order as well as their analytical and numerical solution methods, in which the theory is briefly dealt with before the application examples. In addition, codes show exemplarily how even more demanding questions can be answered and meaningfully represented with the help of a computer algebra system. In the first chapter the necessary previous knowledge from integral and differential calculus is treated. A large number of exercises including solutions round off the work. The Author Prof. (em.) Dr. Albert Fässler studied mathematics at ETH Zurich after studying mechanical engineering and received his doctorate in 1976 with a thesis on applied group theory. In addition to his teaching activities at the ETHZ and his many years of teaching at the Bern University of Applied Sciences, he has also always been internationally active - research stays have taken him to the USA and China, among other places. Since his retirement, he has repeatedly taught in China, India and Switzerland.