International Masterclasses constitute a highly successful program of education and outreach in particle physics for high school students around the world. Sponsored and supported by the International Particle Physics Outreach Group (IPPOG), International Masterclasses reach over 10000 students each year with a simple proposal: be a particle physicist for a day. To that end, the students are ramped up and then given authentic data to analyze in ways that work at their level; they discuss their analysis with physicists, draw conclusions, and meet via videoconference with other students in other parts of the world who have pursued the same studies, moderated by physicists at laboratories where the research happens. Along the way, these students get a look at and feel for what research is like and why it is so exciting.