The working poor of the world are observed to engage in long hours in hard jobs and to work more if wages are further reduced. Mainstream economics brushes off this tendency to increase labour supply as wages fall as perverse because it does not fit the conventional wisdom and tries to explain it as a result of "subsistence mentality", "limited aspiration", or "target income" behaviour of the poor. This however ignores the observed fact that the poor work long hard hours but most of the time, fail to meet their minimum needs of subsistence and live impoverished lives in absolute poverty deficient of both food and physical rest. This book postulates that the observed behaviour is the result of economic distress the working poor suffer and analyses it as a rational behaviour using the conventional utility maximization framework and derives both theoretical and empirical results consistent with the observation. This book aims to correct a serious misconception persisting in the literature relating to the working-poor labour-supply behaviour that is almost universally observed. It also goes onto develop, using the supply function, a methodology to determine the standard of subsistence income and physical rest for the worker.