The aim of our study is to determine the cognitive processes involved in the understanding of the idiomatic expressions in a life-span perspective. The idiomatic expressions are a form of non literal language in which there is a considerable difference between what is said ( literal interpretation) and what is meant ( idiomatic interpretation). The comprehension of these expressions is very context-dependent in which they are produced. So, in our study, we considered the role of the context and the features of these expressions (degree of familiarity and degree of transparency). Five groups of subjects (two groupes of children aged between 6 years and 6 months to 10 years and 6 months, a group of adilescnets aged between 11 years and 17 years, a group of adults aged between 18 and 30 years and a group of elderly persons aged from 60 years and more) participed to the study. We asked them to realize a task of completion of stories (task of understanding of idioms) where every answer must be justified (evaluation of the metapragmatic abilities). This evaluation was completed by tests evaluating the working memory capacities (tasks of verbal span, visuospatial and multimodal) and the executive functions (test of Stroop, Wisconsin Card Sorting Test or WCST and Trail Making Test or TMT). Results underline a context effect and a familiarity effect for the children and the adolescents. Nevertheless, no significant effect of transparency appears. The old subjects, as for them, gave fewer idiomatic answers, in idiomatic context and for the familiar and transparent idioms. Besides, we observe that at the various ages of the life, there are links between the understanding of the idiomatic expressions and the executive functions. However, the executive processes involved are not the same during the development.