The present work seeks for a deeper motivation of those financial market behaviors that remained unexplained by traditional economic theories. It is the result of some years of research in the areas of Behavioral Finance and Market Microstructure. The work undertakes the challenging task of quantifying 'less-rational' aspects of financial decision-making, such as simplified trading rules, emotional reactions, and subjective perceptions and beliefs. To this purpose, not only are traditional models extended in order to account for behavioral elements, but also new models and measures are developed and tested by means of numerical simulations. Surprisingly, it appears that rational trading is not the only way to make money, and the presence of less-than-perfectly rational traders can be compatible with stable and efficient markets. Not only trading decisions but also investment decisions are highly sensitive to subjective attitudes. The work helps to identify several trading and investment strategies that ensure the success and survival of their users and maximize their risky holdings, respectively.