The book is a true knowledge-enhancing project, dealing with the forms of rationality at work in social life, which are so many, varied and complex. Published already in Spanish and Italian, it analyses the role played by rationality through the lens of social theories in order to propose a problematic interpretation of human action. Since there is nothing more practical than a good theory when seeking to understand our society, the book reflects on the theoretical approaches that provide useful categories by means of which to understand and interpret individual, organizational, and institutional action. It proposes an analysis of a wide variety of classics by eminent European and Anglo-American thinkers, such as Dahrendorf, Mannheim, Marx, Popper, Weber, Habermas, Luhmann, Machiavelli, Pareto, Ardigò, Cesareo, Parsons, Schütz, Alexander, Bauman, Beck, Sennett, Antiseri, Boudon, Sen, Simon, to shed light on the relationship between rationality, difficulties in thinking and extra-rationality. Finally, the reasons for unexpected action are investigated as well as the strategic role played by ethics, rationality and skills in postmodern societies on the basis of the contributions of Nussbaum and Piketty.