Communicative competence depends in part – in a significant part – on the ability of speakers and writers to activate lexical resources and to use them functionally in the spoken and written texts they produce. Secondary school students, up to the final years of their studies (and then, in some cases, in the early years of university), sometimes show that they have a limited mastery of vocabulary – specialist, but also common – and a limited awareness of the passing of constraints, both structural and practical, linking words into a large network. In addition, they are often unable to make full use of the resources made available by moderated lexicography. This document, partly thanks to the educational activities proposed (and partly carried out), is intended to contribute to improving knowledge of the vocabulary, improving lexical competence and enhancing the ability to use dictionaries of use, synonyms, analogue dictionaries and placement dictionaries; it also presents less frequent tools for use in high school, but not helpful in language teaching: historical dictionaries and ethymological dictionaries.