Aim of this paper is the analysis of the interrelations among internal labour markets, the structure of skills and training, technology and institutions. After a brief survey of both the empirical and theoretical standard approaches, which tend to stress the relevance of labour market flexibility to decrease the level of unemployment, a framework of analysis is developed in order to discuss the effects of policies aimed at increasing the flexibility of the labour market. The approach followed is based on the institutionalist analysis of labour markets due to some papers of Aoki, Pagano, Sestito and Trento. In this part of the paper three different types of labour market are analysed: the occupational labour market, the internal labour market and the external labour market. In each market a specific pattern of relations among skills, training and institutions prevails. Their characteristics in terms of both functional and numerical flexibility are investigated. At last, in the light of this analysis, some conclusions about the effects of policies aimed at strengthening labour market flexibility are drawn.