The aim of this paper is to examine, both at partial and general equilibrium, the consequences of work sharing policies, when the wages, the length of the working time and the participation rates are endogenous, in an economy where workers get utility from leisure. It is shown that the effects of a shorter working time are very different at the firm level and at the aggregate level. At a steady state, a decrease in working-time is likely to increase employment at the firm level, but reduces employment and welfare at the aggregate level.