MIT mathematician Lawrence D. Guth opens his course 18.156, Projection Theory, by laying out the field's central questions. The lecture introduces projections of sets in the plane and in higher-dimensional space, and frames the exceptional set problem, the question of how small the set of bad projection directions can be for a given set. Guth sketches why projections matter across combinatorics, geometric measure theory, and harmonic analysis, and previews the kinds of theorems the course will build toward, including Falconer-type results. Running 78 minutes, the session stays at the blackboard, with Guth working through definitions and motivating examples rather than formal proofs, setting up the technical machinery that later lectures will develop. It is the first lecture in MIT's Spring 2025 offering of 18.156, aimed at students with a background in real analysis and measure theory.