A3 thinking is a problem-solving and mentoring method from Toyota that forces an entire story — background, current condition, goal, root-cause analysis, countermeasures, plan, and follow-up — onto a single A3-size (11×17") sheet of paper.
The constraint is the point: it demands clarity, evidence, and conciseness, and it doubles as a coaching tool where a mentor develops a problem-solver through iterative review. It is closely tied to PDCA thinking.