In the field of investing, theoretical insights and practical application are surprisingly far apart. On one side is research with its extremely interesting findings, while on the other side is the army of private investors and advisors who hardly take notice of scientific results and continue to make claims that have long been disproven. Against this backdrop, we have compiled ten principles of sound investing. Some are brilliantly simple (Prof. Dr. Martin Weber), but above all, they reflect the current state of financial market research and address practical questions relevant to investors: Does the capital gains tax always reduce returns? What fees are included in different investment forms? How should one plan investment horizons and risk diversification? Dr. Hannes Peterreins provides useful answers and easily implementable tips.