This lecture will discuss a double-sided view of the relationship between the digital revolution and demographic behaviour. In the first part, we will discuss some examples based on ‘digital breadcrumbs’ that people leave online, on how we can exploit the digital revolution to gather new information about demographic behaviour. In the second part, we will consider theoretical mechanisms and empirical evidence on how the digital revolution – and in particular the spread of the Internet – influences demographic behaviour. Both parts are informative about the emerging centrality of the digital revolution for demography today. The Demography Today lecture series aims to promote and communicate scientific work on demography through the dissemination of research and the training of specialists in issues related to demography, Big Data, longitudinal records and health, while informing society, in an accessible way, about issues currently in the foreground of scientific and political debate, such as the limits to longevity, pension systems, aging, emerging diseases, migration and low fertility. This lecture series enjoys the exclusive support of the BBVA Foundation and has been co-organized with the Spanish National Research Council and the LONGPOP project (Methodologies and Data Mining Techniques for the Analysis of Big Data based on Longitudinal Population and Epidemiological Registers). The LONGPOP project has received funding from the European Union’s Horizon 2020 programme.