Project-based science (PBS) is finding a place in more and more secondary school science programs as teachers discover its power to engage students and develop critical-thinking skills. PBS is firmly rooted in constructivism—the idea that individuals construct knowledge individually, through active and meaningful interactions with their environment, rather than by passively receiving transmitted information. PBS is also strongly indebted to the somewhat more obscure "constructionism," which, inspired by constructivism, suggests that learning is an active process and students learn most effectively when they are constructing a meaningful product. This month's column discusses the benefits of doing science with PBS.