In both Québec and France, the demographic structure of the workforce is changing while significant changes are also taking place in the organization of firms. Indeed, the evolving working conditions could put aging workers - whose numbers are growing - in a difficult position. In this article, we draw on various disciplines - mainly sociology, ergonomics and epidemiology - to bring together and discuss the results of recent studies conducted on this subject in both countries. This article first describes the principal trends observed in the demography of firms and in the dominant characteristics of the world of work. A model for understanding the relationships between age, health and the new forms of work organization is then put forward. ...