The Paris corpus1 was financed by the Agence Nationale de la Recherche, in the context of two research programmes entitled ‘Acquisition du Langage et Grammaticalisation’ (2005–2008, http://anr-leonard.ens-lsh.fr/) and ‘Communi- cation Langagie`re chez le Jeune Enfant’ (CoLaJE, 2009–2012, http://colaje. risc.cnrs.fr). The aim of the two programmes was to collect new French data and add five new longitudinal corpora to the international database of the CHILDES project (http://childes.psy.cmu.edu/, MacWhinney, 2000), improve researchers’ transcrip- tion and coding systems to enable them to study the emergence and development of grammatical patterns used by children between age one and seven, and compare child and adult speech. The programmes brought together specialists from various fields of language acquisition in order to study language development in the same longitudinal corpus from a multimodal and interdisciplinary perspective. The anal- yses aimed to find regularities in acquisition for each child and across the children.For this Special Issue of the Journal of French Language Studies, all the authors were given the video recordings and transcriptions of the same four longitudinal corpora. The researchers chose to analyse either one or several children within the same data set according to their own field of competence.