The strict period of lockdown that accompanied the first Covid-19 wave in spring 2020 confirmed the key role of industry and motorized travel in greenhouse gas emissions. For example, emissions linked to transport had dropped by nearly 40% in April and May 2020 by comparison with the same period in 2019. Now, in France the transport sector is the biggest emitter of CO2 (and globally it is the second); mobility is therefore a strategic factor in policies to combat climate change and it is essential to fully understand its nature and determinants. This is the aim of the National Mobility and Ways of Life Survey of the Forum vies mobiles [Mobile Lives Forum] and this article lays out that survey’s significance and methodology, together with the main lessons to be drawn from its 2020 edition. Seeking to be more complete than the National Transport Surveys, currently seen as the authoritative data source in France, the Forum vies mobiles’ survey takes into account “all the trips made at least once every fortnight, whatever the distance of journey and whether or not they occur during the working day.” This definition shows the extent to which the daily journeys taken by French people are currently undercounted and the impact of their lifestyles underestimated, even though these are essential levers in the process of ecological transition. The authors particularly stress the central place of work in the mobility of the French population, not only in terms of travel from home to work, but also of trips made as part of work that are not currently taken into account in the studies on which public policies are based. Lastly, and most importantly, their survey highlights the high degree of variance in the nature of, and reasons for, travel among the French population, depending on their working lives, place of residence etc. and hence the need, if behaviour around mobility is actually to be changed, to design policies that are targeted and not general.