This chapter surveys Gabriel Marcel’s critique of technocratic rationalism. An important figure in French existentialism, Marcel (1889-1973) did not deny the benefits of technological progress. He did worry, though, that a technical ethos was reshaping how we see the world and ourselves. He especially worried about a tendency to reduce mysteries to problems. A problem, for Marcel, is something external to us that can be determinatively understood and solved with a generalizable technique. A mystery, on the other hand, is something in which we are inextricably involved. It has roots deep within us, but it also reaches beyond us. While a problem can be definitively solved, a mystery can only be navigated in light of the concrete situation and the people involved. He worried about the reduction of humans to their “functions,” and he worried about an increasing tendency to treat the central mysteries of human existence—namely love and death—as problems.