This article deals with the problem of the intergenerational transmission of the knowledge of expert employees towards young workers. It is based on an empirical study carried out among five companies that implement a policy linked to the "generation contracts" of the law of 1 March 2013. It can be seen that the circulation of knowledge between generations and its modalities weakens the paths Professionals. Looking at the diversity of practices in companies (social networks, collaborative workshops, professional tutorials, expert relays), transmission is seen as a reconstruction of the training of young people in various learning cultures. How can experts pass on their knowledge to young people? What mechanisms can they mobilize? The analysis of learning situations has made it possible to identify the effects of transmission on the recipients, but also on those who transmit. Basically, it is a question which refers to informal knowledge in the professional activity, itself producing experience.