• The Burden of Obstructive Lung Disease (BOLD) study was established to assess the prevalence of chronic airflow obstruction, a key characteristic of chronic obstructive pulmonary disease, and its risk factors in adults (40 years) from general populations across the world.• The baseline study was conducted between 2003 and 2016, in 41 sites across Africa, Asia, Europe, North America, the Caribbean and Oceania, and collected high-quality pre-and post-bronchodilator spirometry from 28 828 participants.• The follow-up study was conducted between 2019 and 2021, in 18 sites across Africa, Asia, Europe and the Caribbean. At baseline, there were in these sites 12 502 participants with high-quality spirometry. A total of 6452 were followed up, with 5936 completing the study core questionnaire. Of these, 4044 also provided high-quality pre-and post-bronchodilator spirometry.• On both occasions, the core questionnaire covered information on respiratory symptoms, doctor diagnoses, health care use, medication use and ealth status, as well as potential risk factors. Information on occupation, environmental exposures and diet was also collected.• Collaborative research proposals and access to data requests should be submitted to Dr Andre FS Amaral [a. amaral@ imperial. ac. uk]. For more information on the BOLD study, please visit [https://www. imperial. ac. uk/nhli/bold].