With the standard works of business administration theory by Walther Busse von Colbe and Gert Lassmann, benchmarks were set until the early 1990s. A multitude of students have learned from the books, which place special emphasis on practical relevance, and have understood important theories. The third volume of business administration theory on investment calculation and investment theory is now presented in its fifth edition, completely updated and revised, authored by Walther Busse von Colbe and Frank Witte. In parallel with the book, the website Investitionstheorie.de provides a learning environment that supports a blended learning approach, thus bringing the standard work into the modern era. The book clearly explains all important connections of investment calculation and investment theory, such as the calculation of net present value.