In the face of chronic youth unemployment, decision makers in many countries are questioning the role and effectiveness of alternance between school-based vocational training and in-company work experience. This notion applies to three very different realities: training courses offered as an alternative to traditional school-based training for youth with low academic levels; training courses aimed at familiarizing participants with the company and applying knowledge acquired through schooling; and the company as primary site for acquiring competence, with theoretical background provided in the school. One difficulty lies in extending the model to more highly skilled jobs. Companies show an increasing tendency to recruit their labor force with higher training on the external market. One educational concern is whether it is preferable to move to a unified training system or maintain a separate vocational track. For alternating training to function properly, the points of view and motivations of the different actors must be considered. Employers have to see an economic advantage for themselves. The success of alternating training depends on support of regional and local authorities, and the national institutional framework should not block local labor market dynamics. Employees' representatives want to be certain that time spent in the company is in fact used for training. The attraction of more high-quality students raises the problems of parity and the upgrading of industrial and manual occupations. (YLB)