In the framework of training representatives and with regard to the reform of representativeness, communication is presented as a strategic issue and a sort of black box for trade union organizations. Analyzing the respective roles of labour institutes, inter-professional unions, federations and confederations (CGT, CGT-FO, CFDT), this article reveals a highly contrasting situation in the training offered, which varies according to the confederations and, within them, according to widely diverse, essentially random factors. Examining them through the lenses of communication and training enables us to further our understanding of what is bundled under the heading 'crisis of trade unionism'?.