The principal aim of this paper is to present an analysis of the factors that influence the dynamics of welfare spells among households. Four sets of variables are distinguished: variables that affect work conditions and individual preferences; variables that influence labour market rationing; parameters of the welfare program and of other social programs. A particular emphasis is put on the dynamic nature of welfare dependency and on the links relating present and future welfare participation. Econometric results applied to Quebec are also discussed. Finally, conclusions from this analysis are drawn concerning the recent welfare reform proposed by the Quebec Government.