A century ago, life expectancy was roughly 40 years, hence saving for retirement was not an important economic issue. Nowadays, life expectancy exceeds 80 years in many countries, and one should expect to live and consume many years after retirement. Thus, optimizing investments and savings for retirement, with a long planned investment horizon, has become an issue of crucial importance. How should individuals invest for the long run? Does the optimal asset allocation between risky stocks and relatively safer bonds change with age? Is the idiom "stocks for the long run" backed by scientific evidence? This book provides a comprehensive in-depth review of these issues, bridging theory and practice of investments for various horizons.