This masterclass aims at offering an entrance door to the wide field of relative trace formulas, from different perspectives and with different applications ranging from representation theory to analytic number theory. Relative trace formulas are fundamental tools, and we bring together world-class experts to make them shine. The school will consist of three lecture series supplemented by problem sessions and further talks all related to different aspects of this area. The masterclass is mostly intended to graduate students and young researchers, but everyone interested in relative trace formulas is welcome!