International Masterclasses (IMC) is an annual programme for high school students organized by the International Particle Physics Outreach Group (IPPOG) in collaboration with universities and research centres around the globe. In a single day, the students are fully immersed in the activities and challenges of modern research. From morning lectures to afternoon hands-on measurements with real data from large experiments, they have the opportunity to listen to scientists, ask questions and seek professional guidance in solving problems during the data analysis. At the end of the day, the students from several countries join the video conference to discuss their results at the international level. The IMC physics topics include all major LHC experiments, Belle II, Particle Therapy Masterclass, Minerva and, the latest addition, Pierre Auger Masterclass. IMC continue their geographical expansion and currently attract more than 14 000 students from 60 countries. We describe the main features of the programme including its growing physics scope.