The idea of providing an unconditional basic income to every individual, rich or poor, active or inactive, has become one of the most widely debated social security proposals. It is necessary to distinguish between two different concepts of basic income which have gained ground over the last few years. According to the one, a living income should be granted to all citizens in addition to any kind of earned income and independently of the quantity and quality of work actually performed. The second one is a form of social assistance. It differs from the first type in being conceived at the household level, targeted at the poor and being conditional on job search or job acceptance. The first concept of basic income that raises questions from constitutional, social and ethical point of view which require us to question the compatibility of this notion with representative democracy.