This paper identifies a broad concept of unused labour force. This concept can be related to the transitional labour market theory. It is next reviewed in the light of economic studies using a similar construct. Pro’s and con’s of our approach are discussed and the literature is used to assess characteristics of groups building this concept and to identify transition from these groups to (more) employment. A first assessment of the size and some of the main characteristics of such groups is made using the Dutch Labour Force Survey of Statistics Netherlands. As far as transitions are concerned, international studies imply flows of persons from such different groups into labour will almost unavoidably have to be identified using linked longitudinal surveys among individuals. These are currently under construction at Statistics Netherlands.