This report presents the findings from an experience sampling method (ESM) study conducted in Belgium and Finland. The aim of this study was to examine adolescents’ situational and daily information and communications technology (ICT) use and its associations with wellbeing. In both countries, the study was conducted in two waves, during the early and late autumn 2022, respectively. In addition, a supplementary data collection was carried out in Finland in spring 2023. The data consists of 17,671 momentary and daily questionnaire responses from 456 participants. The participants were 13- to 17-year-old adolescents (63% girls) from seven different schools. ESM, a momentary survey method, was used to collect data in situ with participants’ mobile phones. Four momentary and two diary questionnaires were administered during the 14-day data collection period in each wave. The method allows assessing experiences and behaviour that are situational and context-specific, reducing retrospective bias. Moreover, ESM allowed collecting data from a variety of topics by administering both momentary and daily questionnaires. The study was concerned with assessing adolescents’ specific forms of technology use, such as interacting with others by messaging or browsing websites, rather than focusing on screentime or use of specific apps. Additionally, the psychological wellbeing of participants was examined by assessing their affective states. Participants were also requested to report on their sleep daily. Other topics of interest were daily online experiences and activities related to news and comments, problematic social media use, self-determination in ICT use, and face-to-face interaction.