This volume is the fourth in the series "New Materials for a Reality-Based Mathematics Education." It contains a collection of updated and revised contributions to the ISTRON publication series from the past 25 years, which we found to be particularly fruitful and inspiring, serving as a "Best of" for this series. Since 1991, there has been a German-speaking ISTRON group aimed at integrating modeling and real-world references into everyday mathematics education. Since then, the ISTRON group has been publishing a series of materials for reality-based mathematics education. This series is aimed at mathematics educators in schools and universities, as well as students and instructors in continuing education. The contributions demonstrate how to implement mathematical applications and modeling in everyday mathematics teaching.