ISSYP is an exciting and challenging two-week online program for Canadian and international high school students with a keen interest in theoretical physics who intend to pursue physics at the university level. Operated by Perimeter Institute for Theoretical Physics, ISSYP is now in its 20th year and includes over 900 alumni in 60 countries. Over two weeks of online activity: - Mini-courses — These short sessions provide a sound conceptual introduction to the profound and revolutionary ideas at the foundations of modern physics, including topics like quantum mechanics, special relativity, cosmology, general relativity, and black holes. They will include: 1. Independent work conducted before scheduled live sessions — mandatory preparation will include background reading, sample problems, and viewing of recorded lectures. 2. Interactive online sessions — scheduled live sessions will include instructor-led content, lots of time for questions, and group work in breakout rooms. 3. Hands-on tasks — complete simple experiments from home. - Keynote sessions — Perimeter Institute researchers will discuss their work, providing a window into the deep mysteries facing 21st-century theoretical physicists, with lots of time for questions. - Career insight— ISSYP alumni and researchers at different career points will answer questions about university, research careers, and “Life as a Physicist”. - Connection to like-minded peers — Past participants indicate that meeting other future theoretical physicists is a valuable part of ISSYP. The program includes breaks from the scientific content to get to know one another and build relationships that last beyond the program dates.